public function revoke_api_key( $user_id = 0 ) {

    if( empty( $user_id ) ) {
      return false;
    }

    $user = get_userdata( $user_id );

    if( ! $user ) {
      return false;
    }

    $public_key = $this->get_user_public_key( $user_id );
    $secret_key = $this->get_user_secret_key( $user_id );
    if ( ! empty( $public_key ) ) {
      delete_transient( md5( 'edd_api_user_' . $public_key ) );
      delete_transient( md5('edd_api_user_public_key' . $user_id ) );
      delete_transient( md5('edd_api_user_secret_key' . $user_id ) );
      delete_user_meta( $user_id, $public_key );
      delete_user_meta( $user_id, $secret_key );
    } else {
      return false;
    }

    return true;
  }