Keycloak authentication

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

Hi
my problem is that I can't find out how to login with keycloak, I searched a lot and couldn't make it work.
I know in backend, parse server should config for support Keycloak and in front user should login/signup with method linkWith. but the problem is that I get [403] -> unauthorized error with any payload.

Steps to reproduce

Backend:

const fs = require('fs');
const express = require('express');
const ParseServer = require('parse-server').ParseServer;
const cors = require('cors');

const app = express();
app.use(express.json());
app.use(express.text());

const api = new ParseServer({
  databaseURI: 'mongodb://admin:admin@localhost:27017/', // Connection string for your MongoDB database
  cloud: './cloud/main.js', // Path to your Cloud Code
  appId: 'myAppId',
  masterKey: 'myMasterKey', // Keep this key secret!
  fileKey: 'optionalFileKey',
  serverURL: 'http://localhost:8080/parse', // Don't forget to change to https if needed
  auth: {
    keycloak: { 
         config: {
    "realm": "BenjaminR",
    "auth-server-url": "http://localhost:8081/",
    "ssl-required": "external",
    "resource": "my-kc",
    "verify-token-audience": true,
    "credentials": {
      "secret": "KVuKQ47Re25rewsd0RE8lUlaziDtfcDSH"
    },
    "use-resource-role-mappings": true,
    "confidential-port": 0
}
    }
  }
});
app.use(cors('*'));

// Serve the Parse API on the /parse URL prefix
app.use(cors('*'));
app.use('/parse', api);

app.listen(8080, function() {
  console.log('parse-server-example running on port 1337.');
});

Client:

const token = 'keycloak valid and tested token'
const user = new Parse.User();
    await user.linkWith('keycloak', {
      authData: {
        access_token: token,
        id: "cwq613e9-a220-2g7a-bfx7-72722978wc02",
        roles: ["roles..."],
        groups: ["user-groups"]
      }
    });

Actual Outcome

{ "error": "unauthorized" }

Expected Outcome

expected response in document

Server

• Parse Server version: 5.2.8
• Operating system: windows 10
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 6.0.2
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): local (docker)

Client

• SDK (iOS, Android, JavaScript, PHP, Unity, etc): javascript
• SDK version: 3.4.4

Logs

no log

Start with the server's auth.keycloak configuration and the JavaScript Parse.User.linkWith call shown in the issue; reproduce the 403 using the supplied token and Parse Server 5.2.8 setup. Trace the authentication entry point and compare the token fields with the Keycloak integration requirements; done means the cause is isolated and a verified expected response or configuration is documented.