wp_validate_auth_cookie( string $cookie = '', string $scheme = '' )

function wp_validate_auth_cookie($cookie = '', $scheme = '') {
	if ( ! $cookie_elements = wp_parse_auth_cookie($cookie, $scheme) ) {
		/**
		 * Fires if an authentication cookie is malformed.
		 *
		 * @since WP-2.7.0
		 *
		 * @param string $cookie Malformed auth cookie.
		 * @param string $scheme Authentication scheme. Values include 'auth', 'secure_auth',
		 *                       or 'logged_in'.
		 */
		do_action( 'auth_cookie_malformed', $cookie, $scheme );
		return false;
	}

	$scheme = $cookie_elements['scheme'];
	$username = $cookie_elements['username'];
	$hmac = $cookie_elements['hmac'];
	$token = $cookie_elements['token'];
	$expired = $expiration = $cookie_elements['expiration'];

	// Allow a grace period for POST and Ajax requests
	if ( wp_doing_ajax() || 'POST' == $_SERVER['REQUEST_METHOD'] ) {
		$expired += HOUR_IN_SECONDS;
	}

	// Quick check to see if an honest cookie has expired
	if ( $expired < time() ) {
		/**
		 * Fires once an authentication cookie has expired.
		 *
		 * @since WP-2.7.0
		 *
		 * @param array $cookie_elements An array of data for the authentication cookie.
		 */
		do_action( 'auth_cookie_expired', $cookie_elements );
		return false;
	}

	$user = get_user_by('login', $username);
	if ( ! $user ) {
		/**
		 * Fires if a bad username is entered in the user authentication process.
		 *
		 * @since WP-2.7.0
		 *
		 * @param array $cookie_elements An array of data for the authentication cookie.
		 */
		do_action( 'auth_cookie_bad_username', $cookie_elements );
		return false;
	}

	$pass_frag = substr($user->user_pass, 8, 4);

	$key = wp_hash( $username . '|' . $pass_frag . '|' . $expiration . '|' . $token, $scheme );

	// If ext/hash is not present, compat.php's hash_hmac() does not support sha256.
	$algo = function_exists( 'hash' ) ? 'sha256' : 'sha1';
	$hash = hash_hmac( $algo, $username . '|' . $expiration . '|' . $token, $key );

	if ( ! hash_equals( $hash, $hmac ) ) {
		/**
		 * Fires if a bad authentication cookie hash is encountered.
		 *
		 * @since WP-2.7.0
		 *
		 * @param array $cookie_elements An array of data for the authentication cookie.
		 */
		do_action( 'auth_cookie_bad_hash', $cookie_elements );
		return false;
	}

	$manager = WP_Session_Tokens::get_instance( $user->ID );
	if ( ! $manager->verify( $token ) ) {
		do_action( 'auth_cookie_bad_session_token', $cookie_elements );
		return false;
	}

	// Ajax/POST grace period set above
	if ( $expiration < time() ) {
		$GLOBALS['login_grace_period'] = 1;
	}

	/**
	 * Fires once an authentication cookie has been validated.
	 *
	 * @since WP-2.7.0
	 *
	 * @param array   $cookie_elements An array of data for the authentication cookie.
	 * @param WP_User $user            User object.
	 */
	do_action( 'auth_cookie_valid', $cookie_elements, $user );

	return $user->ID;
}