Authenticates and logs a user in with ‘remember’ capability.

The credentials is an array that has ‘user_login’, ‘user_password’, and
‘remember’ indices. If the credentials is not given, then the log in form
will be assumed and used if set.

The various authentication cookies will be set by this function and will be
set for a longer period depending on if the ‘remember’ credential is set to
true.

Note: wp_signon() doesn’t handle setting the current user. This means that if the
function is called before the {@see ‘init’} hook is fired, is_user_logged_in() will
evaluate as false until that point. If is_user_logged_in() is needed in conjunction
with wp_signon(), wp_set_current_user() should be called explicitly.

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'] = wp_unslash( $_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 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 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 ) ) {
		return $user;
	}

	wp_set_auth_cookie( $user->ID, $credentials['remember'], $secure_cookie );
	/**
	 * Fires after the user has successfully logged in.
	 *
	 * @since 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;
}