Looking for a simple approach for handling user $_POST data without AJAX?

Question

I'm looking for a simple way for a Wordpress plugin to process $_POST data from a user submitted form. Back end processing will be performed and then I'll redirect to a new page as appropriate — so during processing there is no UI.

Basically, I want to take a form submit such as...

   <form method="post" action="/back-end-processing.php">
     <input type="text" name="text" />
     <input type="submit" value="submit" />
   </form>';

...and process it like I would with PHP but still be able to use WP's "nonce" protection.

Some examples I've seen suggest that I should use admin-post.php but I was concerned that it should only be used for actual admins and not for general users.

Another approach suggested...

function checkCheckBox()
{
    if($_POST['checkbox'] == 1)
    {
       return true;
    }

    return false;
}

add_action('init', 'checkCheckBox');

...however, this seems like overkill because it will be called for every page while my site visitors will only be posting data to it infrequently.

Answer 1

The best way to process the custom form is the following. If you are using nonce then you don't really have to check $_POST['checkbox'], the code below can be used simply to verify_nonce and then process the form.

function process_my_form() {
    if ( wp_verify_nonce( $_POST['my_nonce_field'], 'my_nonce' ) ) {
        // process your form here
        // you can also redirect and call exit here.
    }
}
add_action( 'init', 'process_my_form' );

But if you still you want to submit your form to a custom php script, then load the wp-blog-header.php.

<?php 
define('WP_USE_THEMES', false);
require('./wp-blog-header.php');
?>

See http://codex.wordpress.org/Integrating_WordPress_with_Your_Website for more information.

Answer 2

Why not use the Settings API, and process the $_POST data inside the validation callback function?

EDIT:

Oh, wait: you said front-end form, which I assume is not related to Plugin options? (If the form does for some reason update Plugin options, see here.)

How are you adding your form? Shortcode? Post data? Hard-coded into the template?