title: Keycloak Custom Validation Output messages
body: <p>I'm using jboss keycloak 1.5 final version.
  I developed my custom user federation provider interfacing with keycloak properties and my user enterprise database. </p>
  
  <p>My need is to send up to user the login interface custom error messages based on particular specific error related to my legacy user db.</p>
  
  <p>I saw keycloak themes have a resources folder by which i can localize and add new messages. Then i can reference them by angular js using </p>
  
  <pre><code>$myMessage
  </code></pre>
  
  <p>notation. The problem is i want to rise up a message from keycloak server. My user federation provider implements UserFederationProvider interface. So i should have to override:</p>
  
  <pre><code>@Override
  public CredentialValidationOutput validCredentials(RealmModel realm, UserCredentialModel credential) {
      LOGGER.info("validCredentials(realm, credential)");
      return CredentialValidationOutput.failed();
  }
  </code></pre>
  
  <p>which seems to be the method i was looking for just because CredentialValidationOutput contains custom messages to be sent as validation output. The problem is this method is never called.</p>
  
  <p>Why?</p>