wp_signon( array $credentials = array(), string|bool $secure_cookie = '' )

function wp_signon( $credentials = array(), $secure_cookie = '' ) {
	if ( empty($credentials) ) {
		$credentials = array(); // Back-compat for plugins passing an empty string.

		if ( ! empty($_POST['log']) )
			$credentials['user_login'] = $_POST['log'];
		if ( ! empty($_POST['pwd']) )
			$credentials['user_password'] = $_POST['pwd'];
		if ( ! empty($_POST['rememberme']) )
			$credentials['remember'] = $_POST['rememberme'];
	}

	if ( !empty($credentials['remember']) )
		$credentials['remember'] = true;
	else
		$credentials['remember'] = false;

	/**
	 * Fires before the user is authenticated.
	 *
	 * The variables passed to the callbacks are passed by reference,
	 * and can be modified by callback functions.
	 *
	 * @since WP-1.5.1
	 *
	 * @todo Decide whether to deprecate the wp_authenticate action.
	 *
	 * @param string $user_login    Username (passed by reference).
	 * @param string $user_password User password (passed by reference).
	 */
	do_action_ref_array( 'wp_authenticate', array( &$credentials['user_login'], &$credentials['user_password'] ) );

	if ( '' === $secure_cookie )
		$secure_cookie = is_ssl();

	/**
	 * Filters whether to use a secure sign-on cookie.
	 *
	 * @since WP-3.1.0
	 *
	 * @param bool  $secure_cookie Whether to use a secure sign-on cookie.
	 * @param array $credentials {
 	 *     Array of entered sign-on data.
 	 *
 	 *     @type string $user_login    Username.
 	 *     @type string $user_password Password entered.
	 *     @type bool   $remember      Whether to 'remember' the user. Increases the time
	 *                                 that the cookie will be kept. Default false.
 	 * }
	 */
	$secure_cookie = apply_filters( 'secure_signon_cookie', $secure_cookie, $credentials );

	global $auth_secure_cookie; // XXX ugly hack to pass this to wp_authenticate_cookie
	$auth_secure_cookie = $secure_cookie;

	add_filter('authenticate', 'wp_authenticate_cookie', 30, 3);

	$user = wp_authenticate($credentials['user_login'], $credentials['user_password']);

	if ( is_wp_error($user) ) {
		if ( $user->get_error_codes() == array('empty_username', 'empty_password') ) {
			$user = new WP_Error('', '');
		}

		return $user;
	}

	wp_set_auth_cookie($user->ID, $credentials['remember'], $secure_cookie);
	/**
	 * Fires after the user has successfully logged in.
	 *
	 * @since WP-1.5.0
	 *
	 * @param string  $user_login Username.
	 * @param WP_User $user       WP_User object of the logged-in user.
	 */
	do_action( 'wp_login', $user->user_login, $user );
	return $user;
}