JWT 토큰 구현

// build.gradle
// implementation 'io.jsonwebtoken:jjwt-api:0.12.3'

@Component
public class JwtUtil {
    @Value("${jwt.secret}")
    private String secret;

    // 토큰 생성
    public String generateToken(String email) {
        return Jwts.builder()
            .subject(email)
            .issuedAt(new Date())
            .expiration(new Date(System.currentTimeMillis() + 1000 * 60 * 15)) // 15분
            .signWith(getKey())
            .compact();
    }

    // 토큰 검증
    public String extractEmail(String token) {
        return Jwts.parser()
            .verifyWith(getKey())
            .build()
            .parseSignedClaims(token)
            .getPayload()
            .getSubject();
    }

    public boolean isValid(String token) {
        try { extractEmail(token); return true; }
        catch (Exception e) { return false; }
    }

    private SecretKey getKey() {
        return Keys.hmacShaKeyFor(secret.getBytes());
    }
}