我假设在打印任何输出之前调用了您的函数，否则重定向将不起作用。

将用户重定向到给定URL的最简单方法是使用：

wp_redirect( $url );
exit;

因此，您的代码可能如下所示：

function authentication($emailAdd, $password) {
            include_once(\'././wp-includes/class-phpass.php\');

        global $wpdb, $formErr;

        if(1 > count($formErr->get_error_messages())){
            $hasher = new PasswordHash(8, TRUE);

            $table = $wpdb->prefix.\'finusers\';
            $results=$wpdb->get_row("SELECT * FROM $table WHERE email_address=\'$emailAdd\'");
            $hashed_pwd = $results->password;
            //echo $hashed_pwd;

            if($hasher->CheckPassword($password, $hashed_pwd)){

                wp_redirect( $url );  // change to correct URL
                exit;

            }else{
                echo "Please check email address of password";
            }
        }
 }

还有，你的代码有很多错误和问题，尽管。。。我真的不会在任何网站上使用它，我想。。。至少不是当前形式。。。请参见下面代码中的我的注释

function authentication($emailAdd, $password) {
        // using ././ won\'t work. It should be ../../. And even that is risky, because the structure may be changed - you should use ABSPATH instead.
        include_once(\'././wp-includes/class-phpass.php\');

        global $wpdb, $formErr;

        // so if there is exactly one error, everything is fine and user can be logged in? ;)
        if(1 > count($formErr->get_error_messages())){
            $hasher = new PasswordHash(8, TRUE);

            $table = $wpdb->prefix.\'finusers\';
            // Why no escaping? What if $emailAdd will contain special characters to perform SQL injection?
            // Another problem is that you query all rows, why no limit?
            $results=$wpdb->get_row("SELECT * FROM $table WHERE email_address=\'$emailAdd\'");
            // And what if there are no such rows? Line below will cause error
            $hashed_pwd = $results->password;
            //echo $hashed_pwd;

            if($hasher->CheckPassword($password, $hashed_pwd)){

                wp_redirect( $url );  // change to correct URL
                exit;

            }else{
                echo "Please check email address of password";
            }
        }
 }