/**
  * Retrieve a user by the given credentials.
  *
  * @param array $credentials
  * @return \Illuminate\Contracts\Auth\Authenticatable|null
  */
 public function retrieveByCredentials(array $credentials)
 {
     if ($this->adldap->authenticate($credentials[$this->usernameField], $credentials['password'])) {
         $userInfo = $this->adldap->user()->info($credentials[$this->usernameField])[0];
         $user = new $this->authModel();
         $user->setAuthIdentifier($userInfo[$this->usernameField][0]);
         return $user;
     }
     return null;
 }