Add refresh token support with /api/auth/refresh endpoint

- RefreshToken entity added with 1-token-per-user logic.
- JWT can be renewed without full login using refresh token.

src/main/java/com/skycrate/backend/skycrateBackend/controller/AuthController.java

@@ -66,4 +66,25 @@ public class AuthController {
 
         return ResponseEntity.ok("Logged out successfully");
     }
+
+    @Autowired
+    private RefreshTokenService refreshTokenService;
+
+    @PostMapping("/refresh")
+    public ResponseEntity<?> refresh(@RequestBody TokenRefreshRequest request) {
+        String requestToken = request.getRefreshToken();
+
+        return refreshTokenService.findByToken(requestToken)
+                .map(token -> {
+                    if (refreshTokenService.isExpired(token)) {
+                        return ResponseEntity.status(403).body("Refresh token expired");
+                    }
+
+                    User user = token.getUser();
+                    String newAccessToken = jwtService.generateToken(user);
+                    return ResponseEntity.ok(new TokenRefreshResponse(newAccessToken, requestToken));
+                })
+                .orElseGet(() -> ResponseEntity.status(403).body("Invalid refresh token"));
+    }
+
 }

src/main/java/com/skycrate/backend/skycrateBackend/dto/TokenRefreshRequest.java

@@ -0,0 +1,13 @@
+package com.skycrate.backend.skycrateBackend.dto;
+
+public class TokenRefreshRequest {
+    private String refreshToken;
+
+    public String getRefreshToken() {
+        return refreshToken;
+    }
+
+    public void setRefreshToken(String refreshToken) {
+        this.refreshToken = refreshToken;
+    }
+}

src/main/java/com/skycrate/backend/skycrateBackend/dto/TokenRefreshResponse.java

@@ -0,0 +1,17 @@
+package com.skycrate.backend.skycrateBackend.dto;
+
+public class TokenRefreshResponse {
+    private String accessToken;
+    private String refreshToken;
+    private String tokenType = "Bearer";
+
+    public TokenRefreshResponse(String accessToken, String refreshToken) {
+        this.accessToken = accessToken;
+        this.refreshToken = refreshToken;
+    }
+
+    // Getters
+    public String getAccessToken() { return accessToken; }
+    public String getRefreshToken() { return refreshToken; }
+    public String getTokenType() { return tokenType; }
+}

src/main/java/com/skycrate/backend/skycrateBackend/entity/RefreshToken.java

@@ -0,0 +1,33 @@
+package com.skycrate.backend.skycrateBackend.entity;
+
+import jakarta.persistence.*;
+import java.time.Instant;
+
+@Entity
+public class RefreshToken {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(nullable = false, unique = true)
+    private String token;
+
+    @OneToOne
+    @JoinColumn(name = "user_id", referencedColumnName = "id")
+    private User user;
+
+    private Instant expiryDate;
+
+    // Getters and setters
+
+    public Long getId() { return id; }
+
+    public String getToken() { return token; }
+    public void setToken(String token) { this.token = token; }
+
+    public User getUser() { return user; }
+    public void setUser(User user) { this.user = user; }
+
+    public Instant getExpiryDate() { return expiryDate; }
+    public void setExpiryDate(Instant expiryDate) { this.expiryDate = expiryDate; }
+}

src/main/java/com/skycrate/backend/skycrateBackend/repository/RefreshTokenRepository.java

@@ -0,0 +1,12 @@
+package com.skycrate.backend.skycrateBackend.repository;
+
+import com.skycrate.backend.skycrateBackend.entity.RefreshToken;
+import com.skycrate.backend.skycrateBackend.entity.User;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.Optional;
+
+public interface RefreshTokenRepository extends JpaRepository<RefreshToken, Long> {
+    Optional<RefreshToken> findByToken(String token);
+    void deleteByUser(User user);
+}

src/main/java/com/skycrate/backend/skycrateBackend/services/RefreshTokenService.java

@@ -0,0 +1,42 @@
+package com.skycrate.backend.skycrateBackend.services;
+
+import com.skycrate.backend.skycrateBackend.entity.RefreshToken;
+import com.skycrate.backend.skycrateBackend.entity.User;
+import com.skycrate.backend.skycrateBackend.repository.RefreshTokenRepository;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+
+import java.time.Instant;
+import java.util.Optional;
+import java.util.UUID;
+
+@Service
+public class RefreshTokenService {
+
+    private final RefreshTokenRepository refreshTokenRepo;
+
+    @Value("${security.jwt.refresh-expiry-ms:604800000}") // 7 days default
+    private Long refreshTokenDurationMs;
+
+    public RefreshTokenService(RefreshTokenRepository refreshTokenRepo) {
+        this.refreshTokenRepo = refreshTokenRepo;
+    }
+
+    public RefreshToken createRefreshToken(User user) {
+        refreshTokenRepo.deleteByUser(user); // Allow only 1 active token per user
+
+        RefreshToken token = new RefreshToken();
+        token.setUser(user);
+        token.setExpiryDate(Instant.now().plusMillis(refreshTokenDurationMs));
+        token.setToken(UUID.randomUUID().toString());
+        return refreshTokenRepo.save(token);
+    }
+
+    public Optional<RefreshToken> findByToken(String token) {
+        return refreshTokenRepo.findByToken(token);
+    }
+
+    public boolean isExpired(RefreshToken token) {
+        return token.getExpiryDate().isBefore(Instant.now());
+    }
+}