protected Users getUsers() {
    return users;
  }
Finds the specific set of {@link UserAuthenticationEntity} instances from the collection of
authentication methods available to the specified {@link UserEntity}.

@param type the {@link UserAuthenticationType} to retrieve
@param key  the key to match on
@return a collection {@link UserAuthenticationEntity} if found; otherwise null
ambari-server/src/main/java/org/apache/ambari/server/security/authentication/AmbariAuthenticationProvider.java