不能使用wp_signon（）

Question

When I try this code

$creds = array( 'user_login' =>  $_POST['benutzername'], 'user_password' => $_POST['passwort'], 'remember' => true );
$user = wp_signon( $creds, false );
if ( is_wp_error($user) ): echo $user->get_error_message(); endif;
wp_set_current_user($user->ID);
return $user;

I get this message:

Warning: Cannot modify header information - headers already sent by (output started at /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/formatting.php:4179) in /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/pluggable.php on line 925 Warning: Cannot modify header information - headers already sent by (output started at /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/formatting.php:4179) in /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/pluggable.php on line 926 Warning: Cannot modify header information - headers already sent by (output started at /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/formatting.php:4179) in /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/pluggable.php on line 927 Catchable fatal error: Object of class WP_User could not be converted to string in /home/httpd/vhosts/your-click.ch/httpdocs/wp-includes/shortcodes.php on line 286

I am using that code in shortcode.php. What's wrong with my code?

Answer 1

According to the WP Manual for the wp_signon function:

This function sends headers to the page. It must be run before any content is returned.

According to the error you get, it seems that you're using this function after some content has being returned already.

Further more, it seems that WP team advise to use that function in the hook after_setup_theme which:

will make it run before the headers and cookies are sent, so it can set the needed cookie for login.