code: public boolean hasCredentials() {
      return credentials.scheme() != null
          && !credentials.scheme().isEmpty()
          && credentials.authToken() != null;
    }
docs: Returns true if this client has non-empty credentials set.  For example, returns {@code false}
  if this client was constructed with {@link Credentials#NONE}.
  
  @return {@code true} if this client is configured with non-empty credentials.