In Keycloak (Server Version 12.0.1), when I try to reach a realm login page, these errors are triggered:

09:44:04,737 ERROR [org.keycloak.headers.DefaultSecurityHeadersProvider] (default task-1) MediaType not set on path /auth/realms/<realm-name>/protocol/openid-connect/auth, with response status 500

09:44:04,738 ERROR [io.undertow.request] (default task-1) UT005023: Exception handling request to /auth/realms/<realm-name>/protocol/openid-connect/auth: java.lang.RuntimeException: java.lang.RuntimeException: org.jboss.resteasy.spi.UnhandledException: javax.ws.rs.InternalServerErrorException: HTTP 500 Internal Server Error

This is the URL generated clicking on Login button on web page (Angular ):

https://auth.<project-name>.local:5001/auth/realms/<realm-name>/protocol/openid-connect/auth?response_type=code&client_id=<client-id>&state=MWl1SkQwNE1vaXZ1LXdLVGh6MWhvZGJiVldPVy40RTJwU2pVfmZ5ZzhsTmRZ&redirect_uri=http%3A%2F%2F<realm-name>%3A4288%2F&scope=openid%20profile%20email%20offline_access%20<clientId>&code_challenge=OPHLi0y4cM0BtILP12xVwUH8p_SiJZjZx1c_ehsFwB4&code_challenge_method=S256&nonce=MWl1SkQwNE1vaXZ1LXdLVGh6MWhvZGJiVldPVy40RTJwU2pVfmZ5ZzhsTmRZ

Angular project

auth.service.ts

public configure() {
authConfig.issuer = this.settingsService.getBaseAuthUrl()}auth/realms/${this._window.location.hostname.split('.')[0]}`;
`this.oauthService.configure(authConfig);

auth.config.ts

export const authConfig: AuthConfig = {
 
  // skipIssuerCheck: null,
  // Url of the Identity Provider
  // issuer: `${authUrl}auth/realms/master`,

  redirectUri: document.getElementsByTagName('base')[0].href as string,

  
  clientId: '<clientId>',
  
  scope: 'openid profile email offline_access <clientId>',

  requireHttps: true,

  showDebugInformation: true,

  responseType: 'code',

  disableAtHashCheck: false    

};

SOLUTION

I solved this problem setting the LoginTheme: keycloak in realm settings.