apply_filters( 'authenticate', null|WP_User|WP_Error $user, string $username, string $password )

617		 *618		 * @param null|WP_User|WP_Error $user     WP_User if the user is authenticated.619		 *                                        WP_Error or null otherwise.620		 * @param string                $username Username or email address.621		 * @param string                $password User password.622		 */623		$user = apply_filters( 'authenticate', null, $username, $password );624 625		if ( null === $user || false === $user ) {626			/*627			 * TODO: What should the error message be? (Or would these even happen?)628			 * Only needed if all authentication handlers fail to return anything.629			 */