Merge branch 'master' into test/add-refresh-tokens

## Add backend refresh tokens

Adds rotating server-side refresh tokens so the access token can be short-lived (5m) without forcing frequent re-login.

- New `POST /api/v1/users/refresh` exchanges the `refreshToken` cookie for a new refresh token and JWT
- Each login starts a token family; reusing a used token after the 5s grace period revokes the whole family
- Logout revokes the family; an hourly job deletes dead families
- Google ID token verification extracted into `GoogleVerifierService`; config moved to a validated `AuthProperties`
- Unauthenticated requests now return 401 instead of 403
- Migration `V2__refresh_tokens.sql` adds `token_families` and `refresh_tokens`

**Breaking changes**
- Cookie `token` renamed to `accessToken` (existing sessions are logged out)
- `/login` and `/refresh` no longer return the JWT in the body, only `{ accessTokenExpiresIn }`
- `jwt.secret.key` / `jwt.expiration` replaced by `app.security.*`; `JWT_SECRET_KEY` must be 32+ chars
- Frontend must call `/refresh` on 401 or before the access token expires

Reviewed-on: #52

pom.xml

@@ -90,6 +90,16 @@
 			<artifactId>spring-boot-starter-test</artifactId>
 			<scope>test</scope>
 		</dependency>
+
+		<!-- Database Migration Tools -->
+		<dependency>
+			<groupId>org.flywaydb</groupId>
+			<artifactId>flyway-core</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.flywaydb</groupId>
+			<artifactId>flyway-database-postgresql</artifactId>
+		</dependency>
 	</dependencies>
 
 	<build>

src/main/java/com/ddf/vodsystem/VodSystemApplication.java

@@ -1,13 +1,16 @@
 package com.ddf.vodsystem;
 
+import com.ddf.vodsystem.dto.properties.AuthProperties;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.scheduling.annotation.EnableAsync;
 import org.springframework.scheduling.annotation.EnableScheduling;
 
 @SpringBootApplication
 @EnableScheduling
 @EnableAsync
+@EnableConfigurationProperties(AuthProperties.class)
 public class VodSystemApplication {
 
 	/**

src/main/java/com/ddf/vodsystem/configuration/SecurityConfig.java

@@ -1,10 +1,12 @@
 package com.ddf.vodsystem.configuration;
 
 import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.security.config.Customizer;
 import org.springframework.security.web.SecurityFilterChain;
+import org.springframework.security.web.authentication.HttpStatusEntryPoint;
 import org.springframework.security.config.http.SessionCreationPolicy;
 import org.springframework.security.config.annotation.web.builders.HttpSecurity;
 import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
@@ -24,7 +26,7 @@ public class SecurityConfig {
 
     /**
      * Builds the security filter chain: stateless sessions, CSRF disabled, the {@link JwtFilter}
-     * installed, and per-endpoint authorization rules.
+     * installed, {@code 401} for unauthenticated requests, and per-endpoint authorization rules.
      *
      * @param http the HTTP security builder to configure
      * @return the built {@link SecurityFilterChain}
@@ -41,11 +43,14 @@ public class SecurityConfig {
                         .requestMatchers("/api/v1/media/compress").permitAll() // compression available without authenticated
                         .requestMatchers("/api/v1/jobs/**").permitAll() // same with jobs
                         .requestMatchers("/api/v1/media/**").authenticated()
-                        .requestMatchers("/api/v1/users/me", "/api/v1/users/logout").authenticated()
-                        .requestMatchers("/api/v1/users/login").permitAll()
+                        .requestMatchers("/api/v1/users/me").authenticated()
+                        // authenticated by the refresh token cookie, not the (possibly expired) access token
+                        .requestMatchers("/api/v1/users/login", "/api/v1/users/refresh", "/api/v1/users/logout").permitAll()
                         .requestMatchers("/api/v1/stream/start", "/api/v1/stream/stop", "/api/v1/stream/heartbeat").permitAll()
                         .anyRequest().authenticated()
                 )
+                // 401 rather than the default 403, so clients know to refresh their session
+                .exceptionHandling(e -> e.authenticationEntryPoint(new HttpStatusEntryPoint(HttpStatus.UNAUTHORIZED)))
                 .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS)
                 );
 

src/main/java/com/ddf/vodsystem/configuration/TimeConfig.java

@@ -0,0 +1,15 @@
+package com.ddf.vodsystem.configuration;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import java.time.Clock;
+
+@Configuration
+public class TimeConfig {
+
+    @Bean
+    public Clock clock() {
+        return Clock.systemUTC();
+    }
+}

src/main/java/com/ddf/vodsystem/controllers/UserController.java

@@ -1,17 +1,21 @@
 package com.ddf.vodsystem.controllers;
 
 import com.ddf.vodsystem.dto.APIResponse;
+import com.ddf.vodsystem.controllers.dto.SessionResponse;
 import com.ddf.vodsystem.controllers.dto.Token;
+import com.ddf.vodsystem.dto.TokenPackage;
+import com.ddf.vodsystem.dto.properties.AuthProperties;
 import com.ddf.vodsystem.entities.User;
 import com.ddf.vodsystem.exceptions.NotAuthenticated;
 import com.ddf.vodsystem.services.UserService;
 import jakarta.servlet.http.HttpServletResponse;
 import jakarta.servlet.http.HttpServletRequest;
-import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.ResponseCookie;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
 
+import java.time.Duration;
 import java.util.Optional;
 
 @RestController
@@ -19,12 +23,18 @@ import java.util.Optional;
 public class UserController {
     private final UserService userService;
 
-    @Value("${jwt.expiration}")
-    private long jwtExpiration;
+    private final Duration jwtExpiration;
+    private final Duration refreshTokenExpiration;
     private static final String SUCCESS = "success";
 
-    public UserController(UserService userService) {
+    private static final String ACCESS_COOKIE_PATH = "/";
+    private static final String REFRESH_COOKIE_PATH = "/api/v1/users";
+
+    public UserController(UserService userService,
+                          AuthProperties props) {
         this.userService = userService;
+        this.jwtExpiration = props.expiration().jwt();
+        this.refreshTokenExpiration = props.expiration().refreshToken();
     }
 
     /**
@@ -47,59 +57,110 @@ public class UserController {
     }
 
     /**
-     * Authenticates a user from a Google ID token and issues a session JWT.
+     * Authenticates a user from a Google ID token and starts a session.
      * <p>
-     * The JWT is set as an HttpOnly {@code token} cookie (scoped by request security) and also
-     * returned in the response body.
+     * Sets two HttpOnly cookies: {@code accessToken} (the JWT, path {@code /}) and {@code refreshToken}
+     * (path {@code /api/v1/users}). Neither token is returned in the response body.
      *
      * @param token    the payload carrying the Google ID token to verify
-     * @param request  the incoming request, used to decide cookie {@code Secure}/{@code SameSite} flags
-     * @param response the response the session cookie is written to
-     * @return {@code 200 OK} wrapping the issued JWT as a {@link Token}
+     * @param request  the incoming request, used to decide the cookies' {@code Secure} flag
+     * @param response the response the cookies are written to
+     * @return {@code 200 OK} wrapping the access token lifetime as a {@link SessionResponse}
+     * @throws NotAuthenticated if the Google ID token is rejected
      */
     @PostMapping("/login")
-    public ResponseEntity<APIResponse<Token>> login(@RequestBody Token token,
+    public ResponseEntity<APIResponse<SessionResponse>> login(@RequestBody Token token,
                                                            HttpServletRequest request,
                                                            HttpServletResponse response) {
-        String jwt = userService.login(token.token());
-
-        ResponseCookie cookie = ResponseCookie.from("token", jwt)
-                .httpOnly(true)
-                .maxAge(jwtExpiration / 1000)
-                .sameSite(request.isSecure() ? "None" : "Lax")
-                .secure(request.isSecure())
-                .path("/")
-                .build();
-
-        response.addHeader("Set-Cookie", cookie.toString());
+        TokenPackage tokenPackage = userService.login(token.token());
+        addCookies(request, response, tokenPackage.accessToken(), tokenPackage.refreshToken());
 
         return ResponseEntity.ok(
-                new APIResponse<>(SUCCESS, "Logged in successfully", new Token(jwt))
+                new APIResponse<>(SUCCESS, "Logged in successfully", sessionResponse())
         );
     }
 
     /**
-     * Logs the user out by clearing the session cookie.
+     * Exchanges the {@code refreshToken} cookie for a new refresh token and JWT, replacing both cookies.
      *
-     * @param response the response the expired cookie is written to
-     * @param request  the incoming request, used to match the original cookie's {@code Secure}/{@code SameSite} flags
+     * @param refreshToken the refresh token from the {@code refreshToken} cookie, if present
+     * @param request      the incoming request, used to decide the cookies' {@code Secure} flag
+     * @param response     the response the new cookies are written to
+     * @return {@code 200 OK} wrapping the new access token lifetime as a {@link SessionResponse}
+     * @throws NotAuthenticated if the refresh token is missing or rejected
+     */
+    @PostMapping("/refresh")
+    public ResponseEntity<APIResponse<SessionResponse>> refresh(
+            @CookieValue(name = "refreshToken", required = false) String refreshToken,
+            HttpServletRequest request,
+            HttpServletResponse response) {
+        TokenPackage tokenPackage = userService.refresh(refreshToken);
+        addCookies(request, response, tokenPackage.accessToken(), tokenPackage.refreshToken());
+
+        return ResponseEntity.ok(
+                new APIResponse<>(SUCCESS, "Refreshed tokens successfully", sessionResponse())
+        );
+    }
+
+    /**
+     * Logs the user out by revoking the session tied to the {@code refreshToken} cookie and clearing
+     * both auth cookies. Succeeds even if no refresh token cookie is present.
+     *
+     * @param refreshToken the refresh token from the {@code refreshToken} cookie, if present
+     * @param request      the incoming request, used to decide the cookies' {@code Secure} flag
+     * @param response     the response the expired cookies are written to
      * @return {@code 200 OK} confirming logout
      */
     @PostMapping("/logout")
-    public ResponseEntity<APIResponse<Void>> logout(HttpServletResponse response,
-		    				    HttpServletRequest request) {
-        ResponseCookie cookie = ResponseCookie.from("token", "")
-                .httpOnly(true)
-                .maxAge(0)
-                .sameSite(request.isSecure() ? "None" : "Lax")
-                .secure(request.isSecure())
-                .path("/")
-                .build();
-
-        response.addHeader("Set-Cookie", cookie.toString());
+    public ResponseEntity<APIResponse<Void>> logout(
+            @CookieValue(name = "refreshToken", required = false) String refreshToken,
+            HttpServletRequest request,
+            HttpServletResponse response) {
+        userService.logout(refreshToken);
+        writeCookies(request, response, "", Duration.ZERO, "", Duration.ZERO);
 
         return ResponseEntity.ok(
                 new APIResponse<>(SUCCESS, "Logged out successfully", null)
         );
     }
+
+    private SessionResponse sessionResponse() {
+        return new SessionResponse(jwtExpiration.getSeconds());
+    }
+
+    private void addCookies(
+            HttpServletRequest request,
+            HttpServletResponse response,
+            String accessToken,
+            String refreshToken) {
+        writeCookies(request, response, accessToken, jwtExpiration, refreshToken, refreshTokenExpiration);
+    }
+
+
+    private void writeCookies(
+            HttpServletRequest request,
+            HttpServletResponse response,
+            String accessToken,
+            Duration accessTokenMaxAge,
+            String refreshToken,
+            Duration refreshTokenMaxAge) {
+        ResponseCookie accessTokenCookie = ResponseCookie.from("accessToken", accessToken)
+                .httpOnly(true)
+                .maxAge(accessTokenMaxAge)
+                .sameSite("Lax")
+                .secure(request.isSecure())
+                .path(ACCESS_COOKIE_PATH)
+                .build();
+
+        ResponseCookie refreshTokenCookie = ResponseCookie.from("refreshToken", refreshToken)
+                .httpOnly(true)
+                .maxAge(refreshTokenMaxAge)
+                .sameSite("Lax")
+                .secure(request.isSecure())
+                .path(REFRESH_COOKIE_PATH)
+                .build();
+
+        response.addHeader(HttpHeaders.SET_COOKIE, refreshTokenCookie.toString());
+        response.addHeader(HttpHeaders.SET_COOKIE, accessTokenCookie.toString());
+    }
 }

src/main/java/com/ddf/vodsystem/controllers/dto/SessionResponse.java

@@ -0,0 +1,11 @@
+package com.ddf.vodsystem.controllers.dto;
+
+/**
+ * Session metadata returned after login or refresh. The tokens themselves are only ever sent as
+ * HttpOnly cookies; this tells the client when to refresh them.
+ *
+ * @param accessTokenExpiresIn seconds until the access token cookie expires
+ */
+public record SessionResponse(
+        long accessTokenExpiresIn
+) {}

src/main/java/com/ddf/vodsystem/dto/GoogleUser.java

@@ -0,0 +1,9 @@
+package com.ddf.vodsystem.dto;
+
+public record GoogleUser(
+        String googleId,
+        String email,
+        String name,
+        String profilePictureUrl
+) {
+}

src/main/java/com/ddf/vodsystem/dto/TokenPackage.java

@@ -0,0 +1,7 @@
+package com.ddf.vodsystem.dto;
+
+public record TokenPackage (
+        String refreshToken,
+        String accessToken
+) {
+}

src/main/java/com/ddf/vodsystem/dto/properties/AuthProperties.java

@@ -0,0 +1,32 @@
+package com.ddf.vodsystem.dto.properties;
+
+import jakarta.validation.Valid;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.validation.annotation.Validated;
+
+import java.time.Duration;
+
+@Validated
+@ConfigurationProperties(prefix = "app.security")
+public record AuthProperties (
+        @NotBlank @Size(min = 32) String jwtSecret,
+        @Valid @NotNull Expiration expiration
+) {
+
+    /**
+     *
+     * @param jwt
+     * @param refreshToken
+     * @param tokenFamily
+     * @param gracePeriod
+     */
+    public record Expiration (
+            @NotNull Duration jwt,
+            @NotNull Duration refreshToken,
+            @NotNull Duration tokenFamily,
+            @NotNull Duration gracePeriod
+    ) {}
+}

src/main/java/com/ddf/vodsystem/entities/RefreshToken.java

@@ -0,0 +1,37 @@
+package com.ddf.vodsystem.entities;
+
+import jakarta.persistence.*;
+import lombok.Data;
+import org.hibernate.annotations.CreationTimestamp;
+
+import java.time.Instant;
+
+@Entity
+@Table(name = "refresh_tokens")
+@Data
+public class RefreshToken {
+    @Id
+    @Column(name = "id", nullable = false, unique = true)
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "family_id", nullable = false)
+    private TokenFamily tokenFamily;
+
+    @Column(name = "token_hash", unique = true, nullable = false, length = 32)
+    private byte[] tokenHash;
+
+    @Column(name = "created_at", nullable = false)
+    @CreationTimestamp
+    private Instant createdAt;
+
+    @Column(name = "expires_at", nullable = false)
+    private Instant expiresAt;
+
+    @Column(name = "used_at")
+    private Instant usedAt;
+
+    @Column(name = "revoked_at")
+    private Instant revokedAt;
+}

src/main/java/com/ddf/vodsystem/entities/TokenFamily.java

@@ -0,0 +1,31 @@
+package com.ddf.vodsystem.entities;
+
+import jakarta.persistence.*;
+import lombok.Data;
+import org.hibernate.annotations.CreationTimestamp;
+
+import java.time.Instant;
+
+@Entity
+@Table(name = "token_families")
+@Data
+public class TokenFamily {
+    @Id
+    @Column(name = "id", nullable = false, unique = true)
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "user_id", nullable = false)
+    private User user;
+
+    @Column(name = "created_at", nullable = false)
+    @CreationTimestamp
+    private Instant createdAt;
+
+    @Column(name = "expires_at", nullable = false)
+    private Instant expiresAt;
+
+    @Column(name = "revoked_at")
+    private Instant revokedAt;
+}

src/main/java/com/ddf/vodsystem/repositories/RefreshTokenRepository.java

@@ -0,0 +1,17 @@
+package com.ddf.vodsystem.repositories;
+
+import com.ddf.vodsystem.entities.RefreshToken;
+import jakarta.persistence.LockModeType;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Lock;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.stereotype.Repository;
+
+import java.util.Optional;
+
+@Repository
+public interface RefreshTokenRepository extends JpaRepository<RefreshToken, Long> {
+    @Lock(LockModeType.PESSIMISTIC_WRITE)
+    @Query("SELECT r FROM RefreshToken r WHERE r.tokenHash = ?1")
+    Optional<RefreshToken> findByHash(byte[] tokenHash);
+}

src/main/java/com/ddf/vodsystem/repositories/TokenFamilyRepository.java

@@ -0,0 +1,30 @@
+package com.ddf.vodsystem.repositories;
+
+import com.ddf.vodsystem.entities.TokenFamily;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Modifying;
+import org.springframework.data.jpa.repository.Query;
+import org.springframework.stereotype.Repository;
+
+import java.time.Instant;
+
+@Repository
+public interface TokenFamilyRepository extends JpaRepository<TokenFamily, Long> {
+    /**
+     * Deletes families that can no longer be refreshed: revoked, expired, or with every refresh
+     * token expired. Their refresh tokens are removed by the {@code ON DELETE CASCADE} foreign key.
+     *
+     * @return the number of families deleted
+     */
+    @Modifying
+    @Query("""
+            DELETE FROM TokenFamily f
+            WHERE f.revokedAt IS NOT NULL
+               OR f.expiresAt <= ?1
+               OR NOT EXISTS (
+                   SELECT 1 FROM RefreshToken r
+                   WHERE r.tokenFamily = f AND r.expiresAt > ?1
+               )
+            """)
+    int deleteDead(Instant now);
+}

src/main/java/com/ddf/vodsystem/security/GoogleAuthConfig.java

@@ -0,0 +1,28 @@
+package com.ddf.vodsystem.security;
+
+import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;
+import com.google.api.client.http.javanet.NetHttpTransport;
+import com.google.api.client.json.gson.GsonFactory;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import java.util.Collections;
+
+@Configuration
+public class GoogleAuthConfig {
+
+    /**
+     * Provides the verifier used to validate Google ID tokens issued for this application's client ID.
+     *
+     * @param googleClientId the OAuth client ID that tokens must be issued for
+     * @return the configured {@link GoogleIdTokenVerifier}
+     */
+    @Bean
+    public GoogleIdTokenVerifier googleIdTokenVerifier(
+            @Value("${spring.security.oauth2.client.registration.google.client-id}") String googleClientId) {
+        return new GoogleIdTokenVerifier.Builder(new NetHttpTransport(), new GsonFactory())
+                .setAudience(Collections.singletonList(googleClientId))
+                .build();
+    }
+}

src/main/java/com/ddf/vodsystem/security/GoogleVerifierService.java

@@ -0,0 +1,49 @@
+package com.ddf.vodsystem.security;
+
+import com.ddf.vodsystem.dto.GoogleUser;
+import com.ddf.vodsystem.exceptions.NotAuthenticated;
+import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
+import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;
+import org.springframework.stereotype.Service;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+
+@Service
+public class GoogleVerifierService {
+    private final GoogleIdTokenVerifier verifier;
+
+    public GoogleVerifierService(GoogleIdTokenVerifier verifier) {
+        this.verifier = verifier;
+    }
+
+    public GoogleUser verify(String idToken) {
+        GoogleIdToken token;
+        try {
+            token = verifier.verify(idToken);
+        } catch (GeneralSecurityException | IOException e) {
+            throw new NotAuthenticated("Invalid ID token: " + e.getMessage());
+        }
+
+        if (token == null) {
+            throw new NotAuthenticated("Invalid ID token");
+        }
+
+        String googleId = token.getPayload().getSubject();
+
+        if (googleId == null) {
+            throw new NotAuthenticated("Google ID does not exist");
+        }
+
+        if (!Boolean.TRUE.equals(token.getPayload().getEmailVerified())) {
+            throw new NotAuthenticated("Email not verified");
+        }
+
+        return new GoogleUser(
+                googleId,
+                token.getPayload().getEmail(),
+                (String) token.getPayload().get("name"),
+                (String) token.getPayload().get("picture")
+        );
+    }
+}

src/main/java/com/ddf/vodsystem/security/JwtFilter.java

@@ -53,7 +53,7 @@ public class JwtFilter extends OncePerRequestFilter {
             Cookie[] cookies = request.getCookies();
             if (cookies != null) {
                 jwt = Arrays.stream(cookies)
-                        .filter(cookie -> "token".equals(cookie.getName()))
+                        .filter(cookie -> "accessToken".equals(cookie.getName()))
                         .map(Cookie::getValue)
                         .findFirst()
                         .orElse(null);

src/main/java/com/ddf/vodsystem/security/JwtService.java

@@ -7,6 +7,7 @@ import com.auth0.jwt.algorithms.Algorithm;
 import com.auth0.jwt.exceptions.JWTDecodeException;
 import com.auth0.jwt.exceptions.TokenExpiredException;
 import com.auth0.jwt.interfaces.DecodedJWT;
+import com.ddf.vodsystem.dto.properties.AuthProperties;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.security.oauth2.jwt.JwtException;
 import org.springframework.stereotype.Service;
@@ -20,10 +21,9 @@ public class JwtService {
     private static final String USER_ID_CLAIM = "userId";
     private static final String ISSUER = "vodsystem";
 
-    public JwtService(@Value("${jwt.secret.key}") String jwtSecretKey,
-                      @Value("${jwt.expiration}") long jwtExpiration) {
-        this.jwtExpiration = jwtExpiration;
-        this.algorithm = Algorithm.HMAC256(jwtSecretKey);
+    public JwtService(AuthProperties props) {
+        this.jwtExpiration = props.expiration().jwt().toMillis();
+        this.algorithm = Algorithm.HMAC256(props.jwtSecret());
     }
 
     /**

src/main/java/com/ddf/vodsystem/security/TokenService.java

@@ -0,0 +1,248 @@
+package com.ddf.vodsystem.security;
+
+import com.ddf.vodsystem.dto.properties.AuthProperties;
+import com.ddf.vodsystem.entities.RefreshToken;
+import com.ddf.vodsystem.entities.TokenFamily;
+import com.ddf.vodsystem.entities.User;
+import com.ddf.vodsystem.exceptions.NotAuthenticated;
+import com.ddf.vodsystem.repositories.RefreshTokenRepository;
+import com.ddf.vodsystem.repositories.TokenFamilyRepository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.scheduling.annotation.Scheduled;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.HexFormat;
+import java.util.Optional;
+
+/**
+ * Issues, rotates and revokes opaque refresh tokens.
+ * <p>
+ * Each login starts a {@link TokenFamily}; every refresh token issued for that session belongs to it.
+ * Only the SHA-256 hash of a token is stored. Presenting an already-used token after the grace
+ * period is treated as theft and revokes the whole family.
+ */
+@Service
+public class TokenService {
+    private static final Logger logger = LoggerFactory.getLogger(TokenService.class);
+    private static final SecureRandom RNG = new SecureRandom();
+    private static final HexFormat HEX = HexFormat.of();
+
+    private final Clock clock;
+
+    private final TokenFamilyRepository tokenFamilyRepository;
+    private final RefreshTokenRepository refreshTokenRepository;
+
+    private final Duration tokenFamilyExpiration;
+    private final Duration refreshTokenExpiration;
+    private final Duration refreshGracePeriod;
+
+    /**
+     * @param tokenFamilyRepository  stores token families (one per login session)
+     * @param refreshTokenRepository stores hashed refresh tokens
+     * @param props                  supplies token family lifetime, refresh token lifetime and reuse grace period
+     * @param clock                  time source for all timestamps and expiry checks
+     */
+    public TokenService (
+            TokenFamilyRepository tokenFamilyRepository,
+            RefreshTokenRepository refreshTokenRepository,
+            AuthProperties props,
+            Clock clock
+    ) {
+        this.tokenFamilyRepository = tokenFamilyRepository;
+        this.refreshTokenRepository = refreshTokenRepository;
+        this.clock = clock;
+
+        this.refreshTokenExpiration = props.expiration().refreshToken();
+        this.tokenFamilyExpiration = props.expiration().tokenFamily();
+        this.refreshGracePeriod = props.expiration().gracePeriod();
+    }
+
+    /**
+     * Starts a new session for a user by creating a token family and its first refresh token.
+     *
+     * @param user the user the session belongs to
+     * @return the raw refresh token as a 64-character hex string; only its hash is persisted
+     */
+    @Transactional
+    public String createSession(User user) {
+        Instant now = Instant.now(clock);
+
+        TokenFamily tokenFamily = new TokenFamily();
+        tokenFamily.setUser(user);
+        tokenFamily.setCreatedAt(now);
+        tokenFamily.setExpiresAt(now.plusMillis(tokenFamilyExpiration.toMillis()));
+        tokenFamilyRepository.save(tokenFamily);
+
+        byte[] token = generateRandomBytes(32);
+
+        createRefreshToken(
+                token,
+                tokenFamily
+        );
+
+        return HEX.formatHex(token);
+    }
+
+    /**
+     * Exchanges a refresh token for a new one in the same family.
+     * <p>
+     * The presented token is marked used and a new token is issued. Presenting a used token again
+     * within the grace period returns another new token without extending the grace period. Presenting
+     * it after the grace period revokes the family; this revocation is committed even though the
+     * method throws.
+     *
+     * @param hexToken the raw refresh token as a hex string
+     * @return the owning user's ID and the new raw refresh token
+     * @throws NotAuthenticated if the token is missing, malformed, unknown, expired, belongs to a revoked
+     *                          or expired family, or is reused after the grace period
+     */
+    @Transactional(noRollbackFor = NotAuthenticated.class)
+    public Rotation rotate(String hexToken) {
+        if (hexToken == null || hexToken.isBlank()) {
+            throw new NotAuthenticated("Missing refresh token");
+        }
+
+        byte[] hash;
+        try {
+            hash = sha256(HEX.parseHex(hexToken));
+        } catch (IllegalArgumentException e) {
+            throw new NotAuthenticated("Malformed refresh token");
+        }
+
+        Instant now = Instant.now(clock);
+
+        // Check Token is real
+        RefreshToken refreshToken = refreshTokenRepository.findByHash(hash)
+                .orElseThrow(() -> new NotAuthenticated("No such refresh token"));
+
+        // Find Token Family
+        TokenFamily tokenFamily = refreshToken.getTokenFamily();
+
+        if (tokenFamily.getRevokedAt() != null) {
+            throw new NotAuthenticated("Token family has been revoked");
+        }
+
+        // Reuse Check
+        if (refreshToken.getUsedAt() != null && now.isAfter(refreshToken.getUsedAt().plus(refreshGracePeriod))) {
+            tokenFamily.setRevokedAt(now);
+            tokenFamilyRepository.save(tokenFamily);
+            throw new NotAuthenticated("Refresh token already being used");
+        }
+
+        // Expiry Check
+        if (
+                now.isAfter(refreshToken.getExpiresAt()) ||
+                now.isAfter(tokenFamily.getExpiresAt())
+        ) {
+            throw new NotAuthenticated("Refresh token or family expired");
+        }
+
+        // Invalidate old token, unless we're within the grace period, otherwise the grace gets extended
+        if (refreshToken.getUsedAt() == null) {
+            refreshToken.setUsedAt(now);
+            refreshTokenRepository.save(refreshToken);
+        }
+
+        byte[] newRawToken = generateRandomBytes(32);
+        createRefreshToken(
+                newRawToken,
+                tokenFamily
+        );
+
+        return new Rotation(tokenFamily.getUser().getId(), HEX.formatHex(newRawToken));
+    }
+
+    /**
+     * Revokes a refresh token and its whole token family, ending the session. Does nothing if the
+     * token is missing or unknown, and leaves existing revocation timestamps unchanged.
+     *
+     * @param hexToken the raw refresh token as a hex string, may be {@code null}
+     * @throws NotAuthenticated if the token is not valid hex
+     */
+    @Transactional
+    public void revoke(String hexToken) {
+        if (hexToken == null || hexToken.isBlank()) return;
+
+        byte[] hash;
+        try {
+            hash = sha256(HEX.parseHex(hexToken));
+        } catch (IllegalArgumentException e) {
+            throw new NotAuthenticated("Malformed refresh token");
+        }
+
+        Optional<RefreshToken> found = refreshTokenRepository.findByHash(hash);
+        if (found.isEmpty()) return;
+
+        Instant now = Instant.now(clock);
+        RefreshToken refreshToken = found.get();
+        TokenFamily family = refreshToken.getTokenFamily();
+
+        if (family.getRevokedAt() == null) {
+            family.setRevokedAt(now);
+            tokenFamilyRepository.save(family);
+        }
+
+        if (refreshToken.getRevokedAt() == null) {
+            refreshToken.setRevokedAt(now);
+            refreshTokenRepository.save(refreshToken);
+        }
+    }
+
+    /**
+     * Scheduled cleanup that deletes token families that can no longer be refreshed, along with all
+     * their refresh tokens.
+     * <p>
+     * Runs hourly. Used tokens in live families are kept, since reuse detection needs them.
+     */
+    @Scheduled(fixedDelay = 3_600_000)
+    @Transactional
+    public void deleteDeadSessions() {
+        int deleted = tokenFamilyRepository.deleteDead(Instant.now(clock));
+        if (deleted > 0) logger.info("Deleted {} dead token families", deleted);
+    }
+
+    /**
+     * Result of a successful {@link #rotate(String)}.
+     *
+     * @param userId          ID of the user who owns the token family
+     * @param newRefreshToken the newly issued raw refresh token as a hex string
+     */
+    public record Rotation(Long userId, String newRefreshToken) {}
+
+    private static byte[] sha256(byte[] in) {
+        try {
+            return MessageDigest.getInstance("SHA-256").digest(in);
+        } catch (NoSuchAlgorithmException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
+    private byte[] generateRandomBytes(int length) {
+        byte[] bytes = new byte[length];
+        RNG.nextBytes(bytes);
+        return bytes;
+    }
+
+
+    private RefreshToken createRefreshToken(
+            byte[] token,
+            TokenFamily tokenFamily
+    ) {
+        Instant now = Instant.now(clock);
+
+        RefreshToken refreshToken = new RefreshToken();
+        refreshToken.setTokenFamily(tokenFamily);
+        refreshToken.setTokenHash(sha256(token));
+        refreshToken.setCreatedAt(now);
+        refreshToken.setExpiresAt(now.plusMillis(refreshTokenExpiration.toMillis()));
+        return refreshTokenRepository.save(refreshToken);
+    }
+}

src/main/java/com/ddf/vodsystem/services/UserService.java

@@ -1,47 +1,44 @@
 package com.ddf.vodsystem.services;
 
+import com.ddf.vodsystem.dto.GoogleUser;
+import com.ddf.vodsystem.dto.TokenPackage;
 import com.ddf.vodsystem.entities.User;
 import com.ddf.vodsystem.exceptions.NotAuthenticated;
 import com.ddf.vodsystem.repositories.UserRepository;
+import com.ddf.vodsystem.security.GoogleVerifierService;
 import com.ddf.vodsystem.security.JwtService;
-import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
-import com.google.api.client.http.javanet.NetHttpTransport;
-import com.google.api.client.json.JsonFactory;
-import com.google.api.client.json.gson.GsonFactory;
-import org.springframework.beans.factory.annotation.Value;
+import com.ddf.vodsystem.security.TokenService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.transaction.annotation.Transactional;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
-import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;
 import org.springframework.stereotype.Service;
 
-import java.io.IOException;
-import java.security.GeneralSecurityException;
 import java.security.SecureRandom;
 import java.time.Instant;
-import java.util.Collections;
 import java.util.HexFormat;
 import java.util.Optional;
 
 @Service
 public class UserService {
-    private final GoogleIdTokenVerifier verifier;
+    private static final Logger logger = LoggerFactory.getLogger(UserService.class);
+
+    private final GoogleVerifierService googleVerifierService;
     private final UserRepository userRepository;
     private final JwtService jwtService;
 
     private static final SecureRandom SECURE_RANDOM = new SecureRandom();
+    private final TokenService tokenService;
 
     public UserService(UserRepository userRepository,
                        JwtService jwtService,
-                       @Value("${google.client.id}") String googleClientId) {
+                       GoogleVerifierService googleVerifierService,
+                       TokenService tokenService) {
         this.userRepository = userRepository;
-
-        NetHttpTransport transport = new NetHttpTransport();
-        JsonFactory jsonFactory = new GsonFactory();
-
-        this.verifier = new GoogleIdTokenVerifier.Builder(transport, jsonFactory)
-                .setAudience(Collections.singletonList(googleClientId))
-                .build();
+        this.googleVerifierService = googleVerifierService;
         this.jwtService = jwtService;
+        this.tokenService = tokenService;
     }
 
     /**
@@ -68,24 +65,58 @@ public class UserService {
     }
 
     /**
-     * Verifies a Google ID token, creating or updating the corresponding user, and issues a session JWT.
+     * Verifies a Google ID token, creates or updates the matching user, and starts a new session.
+     * <p>
+     * A new user gets a username equal to their email, the default role and a random stream key.
+     * Email, name and profile picture are refreshed from Google on every login.
      *
      * @param idToken the Google ID token to verify
-     * @return a signed JWT for the authenticated user
-     * @throws NotAuthenticated if the token is invalid or its subject is missing
+     * @return a new refresh token and a signed JWT access token for the user
+     * @throws NotAuthenticated if the ID token is invalid, has no subject, or its email is unverified
      */
-    public String login(String idToken) {
-        GoogleIdToken googleIdToken = getGoogleIdToken(idToken);
-        String googleId = googleIdToken.getPayload().getSubject();
+    @Transactional
+    public TokenPackage login(String idToken) {
+        GoogleUser googleUser = googleVerifierService.verify(idToken);
+        User user = createOrUpdateGoogleUser(googleUser);
 
-        if (googleId == null) {
-            throw new NotAuthenticated("Invalid ID token");
+        String refreshToken = tokenService.createSession(user);
+        String jwt = jwtService.generateToken(user.getId());
+
+        logger.debug("Access and Refresh tokens issued for User ID {}", user.getId());
+
+        return new TokenPackage(refreshToken, jwt);
     }
 
-        User googleUser = getGoogleUser(googleIdToken);
-        User user = createOrUpdateUser(googleUser);
+    /**
+     * Rotates a refresh token and issues a new JWT access token for its owner.
+     *
+     * @param refreshToken the raw refresh token as a hex string
+     * @return the new refresh token and a signed JWT access token
+     * @throws NotAuthenticated if the refresh token is rejected; see {@link TokenService#rotate(String)}
+     */
+    public TokenPackage refresh(String refreshToken) {
+        TokenService.Rotation rotation = tokenService.rotate(refreshToken);
+        String jwt = jwtService.generateToken(rotation.userId());
 
-        return jwtService.generateToken(user.getId());
+        logger.debug("New refresh and access token issued for user ID {}", rotation.userId());
+
+        return new TokenPackage(rotation.newRefreshToken(), jwt);
+    }
+
+    /**
+     * Ends the session tied to a refresh token by revoking its token family.
+     * Already-issued JWT access tokens stay valid until they expire.
+     *
+     * Does nothing if the token is missing, malformed or unknown.
+     *
+     * @param refreshToken the raw refresh token as a hex string, may be {@code null}
+     */
+    public void logout(String refreshToken) {
+        try {
+            tokenService.revoke(refreshToken);
+        } catch (NotAuthenticated e) {
+            logger.info("Malformed or missing token on logout()");
+        }
     }
 
     /**
@@ -98,51 +129,30 @@ public class UserService {
         return userRepository.findByStreamKey(streamKey);
     }
 
-    private User createOrUpdateUser(User user) {
-        Optional<User> existingUser = userRepository.findByGoogleId(user.getGoogleId());
+    private User createOrUpdateGoogleUser(GoogleUser googleUser) {
+        Optional<User> existingUser = userRepository.findByGoogleId(googleUser.googleId());
+        User user;
 
         if (existingUser.isEmpty()) {
+            user = new User();
+            user.setGoogleId(googleUser.googleId());
+            user.setUsername(googleUser.email());
             user.setRole(0);
             user.setCreatedAt(Instant.now());
-            user.setStreamKey(generateStreamKey());
-            return userRepository.saveAndFlush(user);
+            user.setStreamKey(HexFormat.of().formatHex(generateRandomBytes(24)));
+        } else {
+            user = existingUser.get();
         }
 
-        User existing = existingUser.get();
-        existing.setEmail(user.getEmail());
-        existing.setName(user.getName());
-        existing.setProfilePictureUrl(user.getProfilePictureUrl());
-        existing.setUsername(user.getUsername());
-        return userRepository.saveAndFlush(existing);
+        user.setEmail(googleUser.email());
+        user.setName(googleUser.name());
+        user.setProfilePictureUrl(googleUser.profilePictureUrl());
+        return userRepository.save(user);
     }
 
-    private User getGoogleUser(GoogleIdToken idToken) {
-        String googleId = idToken.getPayload().getSubject();
-        String email = idToken.getPayload().getEmail();
-        String name = (String) idToken.getPayload().get("name");
-        String profilePictureUrl = (String) idToken.getPayload().get("picture");
-
-        User user = new User();
-        user.setGoogleId(googleId);
-        user.setEmail(email);
-        user.setName(name);
-        user.setUsername(email);
-        user.setProfilePictureUrl(profilePictureUrl);
-
-        return user;
-    }
-
-    private GoogleIdToken getGoogleIdToken(String idToken) {
-        try {
-            return verifier.verify(idToken);
-        } catch (GeneralSecurityException | IOException e) {
-            throw new NotAuthenticated("Invalid ID token: " + e.getMessage());
-        }
-    }
-
-    private String generateStreamKey() {
-        byte[] bytes = new byte[24];
+    private byte[] generateRandomBytes(int length) {
+        byte[] bytes = new byte[length];
         SECURE_RANDOM.nextBytes(bytes);
-        return HexFormat.of().formatHex(bytes);
+        return bytes;
     }
 }

src/main/resources/application.properties

@@ -10,17 +10,22 @@ spring.datasource.url=${POSTGRES_URL}
 spring.datasource.username=${POSTGRES_USER}
 spring.datasource.password=${POSTGRES_PASSWORD}
 spring.datasource.driver-class-name=org.postgresql.Driver
-spring.jpa.hibernate.ddl-auto=update
+spring.jpa.hibernate.ddl-auto=validate
 spring.jpa.show-sql=false
-spring.sql.init.mode=always
-spring.sql.init.schema-locations=classpath:db/schema.sql
+
+spring.flyway.enabled=true
+spring.flyway.locations=classpath:db/migrations
 
 ## Security
 spring.security.oauth2.client.registration.google.client-id=${GOOGLE_CLIENT_ID}
 spring.security.oauth2.client.registration.google.client-secret=${GOOGLE_CLIENT_SECRET}
 spring.security.oauth2.client.registration.google.scope=profile,email
-jwt.secret.key=${JWT_SECRET_KEY}
-jwt.expiration=3600000
+app.security.jwt-secret=${JWT_SECRET_KEY}
+
+app.security.expiration.jwt=5m
+app.security.expiration.refresh-token=7d
+app.security.expiration.token-family=90d
+app.security.expiration.grace-period=5s
 
 # Frontend
 frontend.url=${FRONTEND_URL}

src/main/resources/db/migrations/V1__baseline.sql

@@ -1,7 +1,4 @@
--- DROP TABLE IF EXISTS streams;
--- DROP TABLE IF EXISTS clips;
--- DROP TABLE IF EXISTS users;
-
+-- Users Table
 CREATE TABLE IF NOT EXISTS users (
     id BIGSERIAL PRIMARY KEY,
     google_id VARCHAR(64),
@@ -14,6 +11,8 @@ CREATE TABLE IF NOT EXISTS users (
     stream_key VARCHAR(64) NOT NULL UNIQUE
 );
 
+
+-- Streams Table
 CREATE TABLE IF NOT EXISTS streams (
     id BIGSERIAL PRIMARY KEY,
     user_id BIGINT,
@@ -24,6 +23,7 @@ CREATE TABLE IF NOT EXISTS streams (
     FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
 );
 
+-- Clips Table
 CREATE TABLE IF NOT EXISTS clips (
     id BIGSERIAL PRIMARY KEY,
     user_id BIGINT NOT NULL,
@@ -40,6 +40,7 @@ CREATE TABLE IF NOT EXISTS clips (
     FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
 );
 
+-- VoDs Table
 CREATE TABLE IF NOT EXISTS vods (
     id BIGSERIAL PRIMARY KEY,
     user_id BIGINT NOT NULL,
@@ -56,6 +57,7 @@ CREATE TABLE IF NOT EXISTS vods (
     FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
 );
 
+-- Markers Table
 CREATE TABLE IF NOT EXISTS markers (
     id BIGSERIAL PRIMARY KEY,
     user_id BIGINT NOT NULL,

src/main/resources/db/migrations/V2__refresh_tokens.sql

@@ -0,0 +1,27 @@
+CREATE TABLE IF NOT EXISTS token_families
+(
+    id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
+    user_id BIGINT NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    expires_at TIMESTAMPTZ NOT NULL,
+    revoked_at TIMESTAMPTZ
+);
+
+CREATE INDEX IF NOT EXISTS idx_token_families_user_id
+    ON token_families (user_id);
+
+CREATE TABLE IF NOT EXISTS refresh_tokens
+(
+    id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
+    family_id BIGINT NOT NULL REFERENCES token_families (id) ON DELETE CASCADE,
+    token_hash BYTEA NOT NULL UNIQUE, -- unique automatically creates a B-tree index
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    expires_at TIMESTAMPTZ NOT NULL,
+    used_at TIMESTAMPTZ,
+    revoked_at TIMESTAMPTZ,
+
+    CONSTRAINT refresh_tokens_hash_len CHECK (octet_length(token_hash) = 32)
+);
+
+CREATE INDEX IF NOT EXISTS idx_refresh_tokens_family_id
+    ON refresh_tokens (family_id);

src/test/java/com/ddf/vodsystem/security/TokenServiceTest.java

@@ -0,0 +1,628 @@
+package com.ddf.vodsystem.security;
+
+import com.ddf.vodsystem.dto.properties.AuthProperties;
+import com.ddf.vodsystem.entities.RefreshToken;
+import com.ddf.vodsystem.entities.TokenFamily;
+import com.ddf.vodsystem.entities.User;
+import com.ddf.vodsystem.exceptions.NotAuthenticated;
+import com.ddf.vodsystem.repositories.RefreshTokenRepository;
+import com.ddf.vodsystem.repositories.TokenFamilyRepository;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.security.MessageDigest;
+import java.time.*;
+import java.util.HexFormat;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+class MutableClock extends Clock {
+    private Instant now;
+
+    MutableClock(Instant start) {
+        this.now = start;
+    }
+
+    void advance(Duration d) {
+        now = now.plus(d);
+    }
+
+    @Override public Instant instant() { return now; }
+    @Override public ZoneId getZone() { return ZoneOffset.UTC; }
+    @Override public Clock withZone(ZoneId zone) { return this; }
+}
+
+
+@ExtendWith(MockitoExtension.class)
+class TokenServiceTest {
+    @Mock private TokenFamilyRepository tokenFamilyRepository;
+    @Mock private RefreshTokenRepository refreshTokenRepository;
+
+    @Captor ArgumentCaptor<TokenFamily> familyCaptor;
+    @Captor ArgumentCaptor<RefreshToken> tokenCaptor;
+
+    private static final HexFormat HEX = HexFormat.of();
+    private static final String rawToken = "deadbeefdeadbeefdeadbeefdeadbeef";
+
+    AuthProperties authProperties;
+    TokenService tokenService;
+    MutableClock clock;
+
+    User createUser(Long id, String username, String email) {
+        User user = new User();
+        user.setId(id);
+        user.setUsername(username);
+        user.setEmail(email);
+        return user;
+    }
+
+    @BeforeEach
+    void setUp() {
+
+        authProperties = new AuthProperties(
+                "a-secret",
+                new AuthProperties.Expiration(
+                        Duration.ofSeconds(10),
+                        Duration.ofSeconds(10),
+                        Duration.ofSeconds(10),
+                        Duration.ofSeconds(5)
+                )
+        );
+
+        clock = new MutableClock(Instant.parse("2026-01-01T00:00:00Z"));
+
+        tokenService = new TokenService(
+                tokenFamilyRepository,
+                refreshTokenRepository,
+                authProperties,
+                clock
+        );
+    }
+
+    @Nested
+    @DisplayName("createSession()")
+    class createSession {
+        @Test
+        void createSession_createsTokenFamily() {
+            User user = createUser(1L, "user", "user@gmail.com");
+
+            tokenService.createSession(user);
+
+            verify(tokenFamilyRepository).save(familyCaptor.capture());
+            verify(refreshTokenRepository).save(tokenCaptor.capture());
+
+            TokenFamily tokenFamily = familyCaptor.getValue();
+            RefreshToken refreshToken = tokenCaptor.getValue();
+
+            assertSame(tokenFamily.getUser(), user);
+            assertSame(refreshToken.getTokenFamily(), tokenFamily);
+            assertEquals(
+                    tokenFamily.getExpiresAt(),
+                    clock.instant().plusMillis(authProperties.expiration().tokenFamily().toMillis())
+            );
+        }
+
+        @Test
+        void createSession_savesRefreshTokenCreatedAtAndExpires() {
+            User user = createUser(1L, "user", "user");
+
+            tokenService.createSession(user);
+
+            verify(refreshTokenRepository).save(tokenCaptor.capture());
+            RefreshToken refreshToken = tokenCaptor.getValue();
+
+            assertEquals(refreshToken.getCreatedAt(), clock.instant());
+            assertEquals(
+                    refreshToken.getExpiresAt(),
+                    clock.instant().plusMillis(authProperties.expiration().refreshToken().toMillis())
+            );
+        }
+
+        @Test
+        void createSession_returnsHexTokenOf64Characters() {
+            User user = createUser(1L, "user", "user");
+
+            String token = tokenService.createSession(user);
+
+            assertEquals(64, token.length());
+            assertTrue(token.matches("[0-9a-fA-F]+"), () -> "not hex: " + token);
+        }
+
+        @Test
+        void createSession_doesNotStoreRawToken() {
+            User user = createUser(1L, "user", "user");
+
+            String token = tokenService.createSession(user);
+
+            verify(refreshTokenRepository).save(tokenCaptor.capture());
+            RefreshToken refreshToken = tokenCaptor.getValue();
+
+            assertNotEquals(refreshToken.getTokenHash(), HEX.parseHex(token));
+        }
+    }
+
+    // Rotate
+    @Nested
+    @DisplayName("rotate()")
+    class rotate {
+        // Input val
+        @Test
+        void nullToken_throwsNotAuthenticated() {
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> tokenService.rotate(null)
+            );
+        }
+
+        @Test
+        void blankToken_throwsNotAuthenticated() {
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> tokenService.rotate("")
+            );
+        }
+
+        // Invalid cases
+        @Test
+        void unknownToken_throwsNotAuthenticated() {
+            when(refreshTokenRepository.findByHash(any())).thenReturn(
+                    Optional.empty()
+            );
+
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> tokenService.rotate(rawToken)
+            );
+        }
+
+        @Test
+        void revokedFamily_throwsNotAuthenticated() {
+            TokenFamily tokenFamily = activeFamily();
+            tokenFamily.setRevokedAt(Instant.now(clock));
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+
+            clock.advance(Duration.ofMinutes(1));
+
+            when(refreshTokenRepository.findByHash(any())).thenReturn(
+                    Optional.of(refreshToken)
+            );
+
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> tokenService.rotate(rawToken)
+            );
+        }
+
+        // Happy Path
+        @Test
+        void unusedToken_returnsUserIdAndRefreshToken() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+
+            when(refreshTokenRepository.findByHash(any()))
+                    .thenReturn(Optional.of(refreshToken));
+
+            TokenService.Rotation rotation = tokenService.rotate(rawToken);
+
+            assertEquals(1L, rotation.userId());
+            assertNotEquals(rawToken, rotation.newRefreshToken());
+        }
+
+        @Test
+        void unsedToken_savesRefreshToken() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+
+            when(refreshTokenRepository.findByHash(any()))
+                    .thenReturn(Optional.of(refreshToken));
+
+            tokenService.rotate(rawToken);
+
+            verify(refreshTokenRepository, times(2)).save(tokenCaptor.capture());
+
+            RefreshToken newToken = tokenCaptor.getAllValues().stream()
+                    .filter(t -> t.getUsedAt() == null)
+                    .reduce((a, b) -> { throw new AssertionError("expected exactly one unused token saved"); })
+                    .orElseThrow(() -> new AssertionError("no unused token was saved"));
+
+            assertNotEquals(refreshToken.getTokenHash(), newToken.getTokenHash());
+            assertEquals(refreshToken.getTokenFamily().getUser(), newToken.getTokenFamily().getUser());        // same owner
+            assertEquals(refreshToken.getTokenFamily(), newToken.getTokenFamily()); // same rotation family, if you model one
+            assertNull(newToken.getUsedAt());
+        }
+
+        @Test
+        void ununsedToken_savesOldTokenWithUsedAt() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+
+            when(refreshTokenRepository.findByHash(any()))
+                    .thenReturn(Optional.of(refreshToken));
+
+            tokenService.rotate(rawToken);
+
+            verify(refreshTokenRepository, times(2)).save(tokenCaptor.capture());
+
+            RefreshToken savedToken = tokenCaptor.getAllValues().stream()
+                    .filter(t -> t.getUsedAt() != null)
+                    .reduce((a, b) -> { throw new AssertionError("expected exactly one unused token saved"); })
+                    .orElseThrow(() -> new AssertionError("used_at field not set in any token"));
+
+            assertEquals(savedToken.getUsedAt(), clock.instant());
+        }
+
+        @Test
+        void unusedToken_doesNotRevokeFamily() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+
+            when(refreshTokenRepository.findByHash(any()))
+                    .thenReturn(Optional.of(refreshToken));
+
+            tokenService.rotate(rawToken);
+
+            verify(refreshTokenRepository, times(2)).save(tokenCaptor.capture());
+            RefreshToken newToken = tokenCaptor.getAllValues().stream()
+                    .filter(t -> t.getUsedAt() == null)
+                    .reduce((a, b) -> { throw new AssertionError("expected exactly one unused token saved"); })
+                    .orElseThrow(() -> new AssertionError("no unused token was saved"));
+            assertNull(newToken.getTokenFamily().getRevokedAt());
+        }
+
+        @Test
+        void unusedToken_newTokenIsDifferentFromOldToken() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setTokenHash(rawToken.getBytes());
+
+            when(refreshTokenRepository.findByHash(any()))
+                    .thenReturn(Optional.of(refreshToken));
+
+            TokenService.Rotation rotation = tokenService.rotate(rawToken);
+            assertNotEquals(rawToken, rotation.newRefreshToken());
+        }
+
+        // Grace period checks
+        @Test
+        void usedWithinGrace_returnsNewToken() {
+            Instant usedAt = Instant.now(clock);
+
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setTokenHash(rawToken.getBytes());
+            refreshToken.setUsedAt(usedAt);
+
+            when(refreshTokenRepository.findByHash(any()))
+                    .thenReturn(Optional.of(refreshToken));
+
+            // within grace: 3s since usedAt, grace is 5s, and nothing has expired yet
+            clock.advance(Duration.ofSeconds(3));
+
+            TokenService.Rotation rotation = tokenService.rotate(rawToken);
+
+            assertEquals(1L, rotation.userId());
+            assertNotEquals(rawToken, rotation.newRefreshToken());
+            assertNull(tokenFamily.getRevokedAt());
+            verify(tokenFamilyRepository, never()).save(any());
+
+            // grace is not extended by a replay, and only the new token is written
+            assertEquals(usedAt, refreshToken.getUsedAt());
+
+            verify(refreshTokenRepository, times(1)).save(tokenCaptor.capture());
+            RefreshToken newToken = tokenCaptor.getValue();
+            assertNull(newToken.getUsedAt());
+            assertSame(tokenFamily, newToken.getTokenFamily());
+            assertNotEquals(refreshToken.getTokenHash(), newToken.getTokenHash());
+        }
+
+        @Test
+        void usedAtExactGraceBoundary_returnsNewToken() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(authProperties.expiration().gracePeriod());
+
+            TokenService.Rotation rotation = tokenService.rotate(rawToken);
+
+            assertEquals(1L, rotation.userId());
+            assertNull(tokenFamily.getRevokedAt());
+        }
+
+        // Reuse after grace period
+        @Test
+        void usedAfterGrace_throwsNotAuthenticated() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(6));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+        }
+
+        @Test
+        void usedAfterGrace_revokesFamily() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(6));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            verify(tokenFamilyRepository).save(familyCaptor.capture());
+            assertSame(tokenFamily, familyCaptor.getValue());
+            assertEquals(clock.instant(), tokenFamily.getRevokedAt());
+        }
+
+        @Test
+        void usedAfterGrace_doesNotIssueNewToken() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(6));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            verify(refreshTokenRepository, never()).save(any());
+        }
+
+        @Test
+        void usedAfterGrace_subsequentRotateRejectedWithoutResaving() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(6));
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+            verify(tokenFamilyRepository, times(1)).save(any());
+        }
+
+        // Expiry
+        @Test
+        void expiredToken_throwsNotAuthenticated() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setExpiresAt(clock.instant().minusSeconds(1));
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+        }
+
+        @Test
+        void expiredFamily_throwsNotAuthenticated() {
+            TokenFamily tokenFamily = activeFamily();
+            tokenFamily.setExpiresAt(clock.instant().minusSeconds(1));
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+        }
+
+        @Test
+        void expiredToken_doesNotSaveOrRevoke() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(11));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            verify(refreshTokenRepository, never()).save(any());
+            verify(tokenFamilyRepository, never()).save(any());
+            assertNull(refreshToken.getUsedAt());
+            assertNull(tokenFamily.getRevokedAt());
+        }
+
+        @Test
+        void tokenAtExactExpiry_returnsNewToken() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(10));
+
+            TokenService.Rotation rotation = tokenService.rotate(rawToken);
+
+            assertEquals(1L, rotation.userId());
+        }
+
+        // Ordering
+        @Test
+        void revokedFamilyAndUsedAfterGrace_doesNotRevokeAgain() {
+            TokenFamily tokenFamily = activeFamily();
+            Instant revokedAt = clock.instant();
+            tokenFamily.setRevokedAt(revokedAt);
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(6));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            assertEquals(revokedAt, tokenFamily.getRevokedAt());
+            verify(tokenFamilyRepository, never()).save(any());
+        }
+
+        @Test
+        void revokedAndExpiredFamily_throwsNotAuthenticated() {
+            TokenFamily tokenFamily = activeFamily();
+            tokenFamily.setRevokedAt(clock.instant());
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(11));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+        }
+
+        @Test
+        void expiredAndUsedAfterGrace_revokesFamily() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(11));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            assertEquals(clock.instant(), tokenFamily.getRevokedAt());
+            verify(tokenFamilyRepository).save(tokenFamily);
+        }
+
+        @Test
+        void expiredWithinGrace_doesNotRevokeFamily() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setExpiresAt(clock.instant().plusSeconds(2));
+            refreshToken.setUsedAt(clock.instant());
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofSeconds(3));
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            assertNull(tokenFamily.getRevokedAt());
+            verify(tokenFamilyRepository, never()).save(any());
+            verify(refreshTokenRepository, never()).save(any());
+        }
+
+        @Test
+        void unknownToken_doesNotTouchRepositoriesFurther() {
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.empty());
+
+            assertThrows(NotAuthenticated.class, () -> tokenService.rotate(rawToken));
+
+            verify(refreshTokenRepository, never()).save(any());
+            verifyNoInteractions(tokenFamilyRepository);
+        }
+    }
+
+    @Nested
+    @DisplayName("revoke()")
+    class revoke {
+        @Test
+        void knownToken_revokesTokenAndFamily() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            tokenService.revoke(rawToken);
+
+            assertEquals(clock.instant(), tokenFamily.getRevokedAt());
+            assertEquals(clock.instant(), refreshToken.getRevokedAt());
+        }
+
+        @Test
+        void knownToken_savesTokenAndFamily() {
+            TokenFamily tokenFamily = activeFamily();
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            tokenService.revoke(rawToken);
+
+            verify(tokenFamilyRepository).save(tokenFamily);
+            verify(refreshTokenRepository).save(refreshToken);
+        }
+
+        @Test
+        void knownToken_looksUpBySingleSha256Hash() throws Exception {
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.empty());
+
+            tokenService.revoke(rawToken);
+
+            byte[] expectedHash = MessageDigest.getInstance("SHA-256").digest(HEX.parseHex(rawToken));
+            verify(refreshTokenRepository).findByHash(expectedHash);
+        }
+
+        @Test
+        void alreadyRevoked_keepsOriginalTimestampsAndDoesNotSave() {
+            Instant revokedAt = clock.instant();
+            TokenFamily tokenFamily = activeFamily();
+            tokenFamily.setRevokedAt(revokedAt);
+            RefreshToken refreshToken = tokenIn(tokenFamily);
+            refreshToken.setRevokedAt(revokedAt);
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.of(refreshToken));
+
+            clock.advance(Duration.ofMinutes(1));
+            tokenService.revoke(rawToken);
+
+            assertEquals(revokedAt, tokenFamily.getRevokedAt());
+            assertEquals(revokedAt, refreshToken.getRevokedAt());
+            verify(tokenFamilyRepository, never()).save(any());
+            verify(refreshTokenRepository, never()).save(any());
+        }
+
+        @Test
+        void unknownToken_doesNothing() {
+            when(refreshTokenRepository.findByHash(any())).thenReturn(Optional.empty());
+
+            tokenService.revoke(rawToken);
+
+            verify(refreshTokenRepository, never()).save(any());
+            verifyNoInteractions(tokenFamilyRepository);
+        }
+
+        @Test
+        void nullToken_doesNothing() {
+            tokenService.revoke(null);
+
+            verifyNoInteractions(refreshTokenRepository, tokenFamilyRepository);
+        }
+
+        @Test
+        void blankToken_doesNothing() {
+            tokenService.revoke("");
+
+            verifyNoInteractions(refreshTokenRepository, tokenFamilyRepository);
+        }
+
+        @Test
+        void malformedToken_throwsNotAuthenticated() {
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> tokenService.revoke("not-hex")
+            );
+
+            verifyNoInteractions(refreshTokenRepository, tokenFamilyRepository);
+        }
+    }
+
+    private TokenFamily activeFamily() {
+        TokenFamily tokenFamily = new TokenFamily();
+        tokenFamily.setId(1L);
+        tokenFamily.setUser(createUser(1L, "user", "user"));
+        tokenFamily.setExpiresAt(clock.instant().plusSeconds(10));
+        return tokenFamily;
+    }
+
+    private RefreshToken tokenIn(TokenFamily tokenFamily) {
+        RefreshToken refreshToken = new RefreshToken();
+        refreshToken.setTokenFamily(tokenFamily);
+        refreshToken.setExpiresAt(clock.instant().plusSeconds(10));
+        return refreshToken;
+    }
+}

src/test/java/com/ddf/vodsystem/services/UserServiceTest.java

@@ -0,0 +1,295 @@
+package com.ddf.vodsystem.services;
+
+import com.ddf.vodsystem.dto.GoogleUser;
+import com.ddf.vodsystem.dto.TokenPackage;
+import com.ddf.vodsystem.entities.User;
+import com.ddf.vodsystem.exceptions.NotAuthenticated;
+import com.ddf.vodsystem.repositories.UserRepository;
+import com.ddf.vodsystem.security.GoogleVerifierService;
+import com.ddf.vodsystem.security.JwtService;
+import com.ddf.vodsystem.security.TokenService;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+import org.springframework.security.core.context.SecurityContextHolder;
+
+import java.util.List;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+@ExtendWith(MockitoExtension.class)
+class UserServiceTest {
+    @Mock private GoogleVerifierService googleVerifierService;
+    @Mock private JwtService jwtService;
+    @Mock private UserRepository userRepository;
+    @Mock private TokenService tokenService;
+
+    @Captor ArgumentCaptor<User> userCaptor;
+
+    private static final String ID_TOKEN = "google-id-token";
+    private static final String REFRESH_TOKEN = "deadbeefdeadbeefdeadbeefdeadbeef";
+    private static final String NEW_REFRESH_TOKEN = "cafebabecafebabecafebabecafebabe";
+    private static final String JWT = "header.payload.signature";
+    private static final String GOOGLE_ID = "google-id";
+
+    UserService userService;
+
+    User createUser(Long id, String username, String email) {
+        User user = new User();
+        user.setId(id);
+        user.setUsername(username);
+        user.setEmail(email);
+        return user;
+    }
+
+    GoogleUser googleUser() {
+        return new GoogleUser(
+                GOOGLE_ID,
+                "user@example.com",
+                "My User",
+                "https://lol.com/1"
+        );
+    }
+
+    @BeforeEach
+    void setUp() {
+        userService = new UserService(
+                userRepository,
+                jwtService,
+                googleVerifierService,
+                tokenService
+        );
+    }
+
+    @AfterEach
+    void clearSecurityContext() {
+        SecurityContextHolder.clearContext();
+    }
+
+    @Nested
+    @DisplayName("getUserById()")
+    class getUserById {
+        @Test
+        void existingId_returnsUser() {
+            User user = createUser(1L, "user", "user@example.com");
+            when(userRepository.findById(1L)).thenReturn(Optional.of(user));
+
+            Optional<User> result = userService.getUserById(1L);
+
+            assertTrue(result.isPresent());
+            assertSame(user, result.get());
+        }
+
+        @Test
+        void unknownId_returnsEmpty() {
+            when(userRepository.findById(1L)).thenReturn(Optional.empty());
+
+            assertTrue(userService.getUserById(1L).isEmpty());
+        }
+    }
+
+    @Nested
+    @DisplayName("getLoggedInUser()")
+    class getLoggedInUser {
+        @Test
+        void authenticatedUserPrincipal_returnsUser() {
+            User user = createUser(1L, "user", "user@example.com");
+            SecurityContextHolder.getContext().setAuthentication(
+                    new UsernamePasswordAuthenticationToken(user, null, List.of())
+            );
+
+            Optional<User> result = userService.getLoggedInUser();
+
+            assertTrue(result.isPresent());
+            assertSame(user, result.get());
+        }
+
+        @Test
+        void noAuthentication_returnsEmpty() {
+            assertTrue(userService.getLoggedInUser().isEmpty());
+        }
+
+        @Test
+        void unauthenticated_returnsEmpty() {
+            User user = createUser(1L, "user", "user@example.com");
+            SecurityContextHolder.getContext().setAuthentication(
+                    new UsernamePasswordAuthenticationToken(user, null)
+            );
+
+            assertTrue(userService.getLoggedInUser().isEmpty());
+        }
+
+        @Test
+        void nonUserPrincipal_returnsEmpty() {
+            SecurityContextHolder.getContext().setAuthentication(
+                    new UsernamePasswordAuthenticationToken("anonymous", null, List.of())
+            );
+
+            assertTrue(userService.getLoggedInUser().isEmpty());
+        }
+    }
+
+    @Nested
+    @DisplayName("login()")
+    class login {
+        @Test
+        void newUser_savesUserToRepo() {
+            when(googleVerifierService.verify(ID_TOKEN)).thenReturn(googleUser());
+            when(userRepository.findByGoogleId(GOOGLE_ID)).thenReturn(Optional.empty());
+            when(userRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+
+            userService.login(ID_TOKEN);
+
+            verify(userRepository).save(userCaptor.capture());
+            User saved = userCaptor.getValue();
+            assertEquals(GOOGLE_ID, saved.getGoogleId());
+            assertEquals("user@example.com", saved.getEmail());
+            assertEquals("user@example.com", saved.getUsername());
+            assertEquals("My User", saved.getName());
+            assertEquals("https://lol.com/1", saved.getProfilePictureUrl());
+            assertEquals(0, saved.getRole());
+            assertNotNull(saved.getCreatedAt());
+        }
+
+        @Test
+        void newUser_generatesHexStreamKeyOf48Characters() {
+            when(googleVerifierService.verify(ID_TOKEN)).thenReturn(googleUser());
+            when(userRepository.findByGoogleId(GOOGLE_ID)).thenReturn(Optional.empty());
+            when(userRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+
+            userService.login(ID_TOKEN);
+
+            verify(userRepository).save(userCaptor.capture());
+            String streamKey = userCaptor.getValue().getStreamKey();
+            assertEquals(48, streamKey.length());
+            assertTrue(streamKey.matches("[0-9a-f]+"), () -> "not hex: " + streamKey);
+        }
+
+        @Test
+        void existingUser_updatesUserInfo() {
+            User existingUser = createUser(1L, "old-username", "old@example.com");
+            existingUser.setGoogleId(GOOGLE_ID);
+            existingUser.setName("Old Name");
+            existingUser.setProfilePictureUrl("https://lol.com/old");
+            existingUser.setStreamKey("123");
+
+            when(googleVerifierService.verify(ID_TOKEN)).thenReturn(googleUser());
+            when(userRepository.findByGoogleId(GOOGLE_ID)).thenReturn(Optional.of(existingUser));
+            when(userRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+
+            userService.login(ID_TOKEN);
+
+            verify(userRepository).save(userCaptor.capture());
+            User saved = userCaptor.getValue();
+            assertSame(existingUser, saved);
+            assertEquals(1L, saved.getId());
+            assertEquals(GOOGLE_ID, saved.getGoogleId());
+            assertEquals("user@example.com", saved.getEmail());
+            assertEquals("My User", saved.getName());
+            assertEquals("https://lol.com/1", saved.getProfilePictureUrl());
+            assertEquals("old-username", saved.getUsername());
+            assertEquals("123", saved.getStreamKey());
+        }
+
+        @Test
+        void validToken_returnsRefreshTokenAndJwt() {
+            when(googleVerifierService.verify(ID_TOKEN)).thenReturn(googleUser());
+            when(userRepository.findByGoogleId(GOOGLE_ID)).thenReturn(Optional.empty());
+            when(userRepository.save(any())).thenAnswer(inv -> inv.getArgument(0));
+            when(tokenService.createSession(any())).thenReturn(REFRESH_TOKEN);
+            when(jwtService.generateToken(any())).thenReturn(JWT);
+
+            TokenPackage tokenPackage = userService.login(ID_TOKEN);
+
+            assertEquals(REFRESH_TOKEN, tokenPackage.refreshToken());
+            assertEquals(JWT, tokenPackage.accessToken());
+        }
+
+        @Test
+        void validToken_createsSessionForSavedUser() {
+            User savedUser = createUser(42L, "user@example.com", "user@example.com");
+
+            when(googleVerifierService.verify(ID_TOKEN)).thenReturn(googleUser());
+            when(userRepository.findByGoogleId(GOOGLE_ID)).thenReturn(Optional.empty());
+            when(userRepository.save(any())).thenReturn(savedUser);
+
+            userService.login(ID_TOKEN);
+
+            verify(tokenService).createSession(savedUser);
+            verify(jwtService).generateToken(42L);
+        }
+
+        @Test
+        void invalidToken_throwsNotAuthenticated() {
+            when(googleVerifierService.verify(ID_TOKEN))
+                    .thenThrow(new NotAuthenticated("Invalid ID token"));
+
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> userService.login(ID_TOKEN)
+            );
+
+            verifyNoInteractions(userRepository, tokenService, jwtService);
+        }
+    }
+
+    @Nested
+    @DisplayName("refresh()")
+    class refresh {
+        @Test
+        void validToken_returnsRotatedTokenAndJwt() {
+            when(tokenService.rotate(REFRESH_TOKEN))
+                    .thenReturn(new TokenService.Rotation(1L, NEW_REFRESH_TOKEN));
+            when(jwtService.generateToken(1L)).thenReturn(JWT);
+
+            TokenPackage tokenPackage = userService.refresh(REFRESH_TOKEN);
+
+            assertEquals(NEW_REFRESH_TOKEN, tokenPackage.refreshToken());
+            assertEquals(JWT, tokenPackage.accessToken());
+        }
+
+        @Test
+        void invalidToken_throwsNotAuthenticated() {
+            when(tokenService.rotate(REFRESH_TOKEN))
+                    .thenThrow(new NotAuthenticated("Invalid refresh token"));
+
+            assertThrows(
+                    NotAuthenticated.class,
+                    () -> userService.refresh(REFRESH_TOKEN)
+            );
+
+            verifyNoInteractions(jwtService);
+        }
+    }
+
+    @Nested
+    @DisplayName("logout()")
+    class logout {
+        @Test
+        void revokesRefreshToken() {
+            userService.logout(REFRESH_TOKEN);
+
+            verify(tokenService).revoke(REFRESH_TOKEN);
+        }
+
+        @Test
+        void doesNotIssueTokens() {
+            userService.logout(REFRESH_TOKEN);
+
+            verify(tokenService, never()).createSession(any());
+            verify(tokenService, never()).rotate(any());
+            verifyNoInteractions(jwtService);
+        }
+    }
+}