我找到了使用以下函数的解决方案：

    function auto_login() {
        // make sure user is not logged in and "user" was POST\'d
        $username = isset( $_POST[\'user\'] )? $_POST[\'user\'] : false;
        if ( ! is_user_logged_in() && $username ){
            // load the user by username
            $user = get_user_by( \'login\', $username ); 
            if ( $user ) {
                // log user in using the $user object properties
                wp_set_current_user( $user->ID, $user->user_login );
                wp_set_auth_cookie( $user->ID );
                do_action( \'wp_login\', $user->user_login );
            }
        }
    }

add_action( \'wp_loaded\',\'auto_login\' );