JwtService.java

@Service
public class JwtService {
  
  @Autowired
  private JwtEncoder encoder;

  public String generateToken(Authentication authentication) {
    Instant now = Instant.now();
    long expiry = 525600L;

    String roles = authentication
        .getAuthorities().stream()
        .map(GrantedAuthority::getAuthority)
        .collect(Collectors
            .joining(" "));

    JwtClaimsSet claims = JwtClaimsSet.builder()
        .issuer("spring-security-jwt")
        .issuedAt(now)
        .expiresAt(now.plusSeconds(expiry))
        .subject(authentication.getName())
        .claim("scope", roles)
        .build();

    return encoder.encode(
        JwtEncoderParameters.from(claims))
        .getTokenValue();
  }

}