add backend

backend/src/main/java/com/yoyuzh/auth/JwtTokenProvider.java

@@ -0,0 +1,62 @@
+package com.yoyuzh.auth;
+
+import com.yoyuzh.config.JwtProperties;
+import io.jsonwebtoken.Claims;
+import io.jsonwebtoken.Jwts;
+import io.jsonwebtoken.security.Keys;
+import jakarta.annotation.PostConstruct;
+import org.springframework.stereotype.Component;
+
+import javax.crypto.SecretKey;
+import java.nio.charset.StandardCharsets;
+import java.time.Instant;
+import java.util.Date;
+
+@Component
+public class JwtTokenProvider {
+
+    private final JwtProperties jwtProperties;
+    private SecretKey secretKey;
+
+    public JwtTokenProvider(JwtProperties jwtProperties) {
+        this.jwtProperties = jwtProperties;
+    }
+
+    @PostConstruct
+    public void init() {
+        secretKey = Keys.hmacShaKeyFor(jwtProperties.getSecret().getBytes(StandardCharsets.UTF_8));
+    }
+
+    public String generateToken(Long userId, String username) {
+        Instant now = Instant.now();
+        return Jwts.builder()
+                .subject(username)
+                .claim("uid", userId)
+                .issuedAt(Date.from(now))
+                .expiration(Date.from(now.plusSeconds(jwtProperties.getExpirationSeconds())))
+                .signWith(secretKey)
+                .compact();
+    }
+
+    public boolean validateToken(String token) {
+        try {
+            Jwts.parser().verifyWith(secretKey).build().parseSignedClaims(token);
+            return true;
+        } catch (Exception ex) {
+            return false;
+        }
+    }
+
+    public String getUsername(String token) {
+        return parseClaims(token).getSubject();
+    }
+
+    public Long getUserId(String token) {
+        Object uid = parseClaims(token).get("uid");
+        return uid == null ? null : Long.parseLong(uid.toString());
+    }
+
+    private Claims parseClaims(String token) {
+        return Jwts.parser().verifyWith(secretKey).build().parseSignedClaims(token).getPayload();
+    }
+}