code: public KeycloakConfig setSystemProperties()
      {
          if ( !isEnabled() )
          {
              return this;
          }
  
          final Properties properties = System.getProperties();
          properties.setProperty( KEYCLOAK_REALM, getRealm() );
          properties.setProperty( KEYCLOAK_URL, getUrl() );
  
          if ( getServerResource() != null )
          {
              properties.setProperty( KEYCLOAK_SERVER_RESOURCE, getServerResource() );
          }
  
          if ( getServerCredentialSecret() != null )
          {
              properties.setProperty( KEYCLOAK_SERVER_CREDENTIAL_SECRET, getServerCredentialSecret() );
          }
  
          if ( getRealmPublicKey() != null )
          {
              properties.setProperty( KEYCLOAK_REALM_PUBLIC_KEY, getRealmPublicKey() );
          }
  
          System.setProperties( properties );
  
          return this;
      }
docs: Set system properties for keycloak to use when filtering keycloak.json...