JwtTokenEnhancer.java

package com.example.identity.config;

import com.example.identity.model.User;
import org.springframework.security.oauth2.common.DefaultOAuth2AccessToken;
import org.springframework.security.oauth2.common.OAuth2AccessToken;
import org.springframework.security.oauth2.provider.OAuth2Authentication;
import org.springframework.security.oauth2.provider.token.TokenEnhancer;

import java.util.HashMap;
import java.util.Map;

public class JwtTokenEnhancer implements TokenEnhancer {

    @Override
    public OAuth2AccessToken enhance(OAuth2AccessToken accessToken, OAuth2Authentication authentication) {
        Map<String, Object> additionalInfo = new HashMap<>();

        User user = (User) authentication.getUserAuthentication().getPrincipal();
        Integer userId = user.getId();

        
      // Resource Server always throws a 401, cannot validate the token error if this is set here.
      additionalInfo.put("sub", userId);
      // works if it's this is set.
      additionalInfo.put("subject", userId);

        ((DefaultOAuth2AccessToken) accessToken).setAdditionalInformation(additionalInfo);
        return accessToken;
    }
}