Setting GF-form submitted posts to password protected?

Hi All - I'm interested in setting up a pay-to-post mechanism, using the Paypal Add-On, that works like this:
- the form contains post fields and is integrated with Paypal via the Add-On, such that the post is not published until payment is received;
- the redirect for the form is set-up in such a way that, once payment is received, the site redirects the user to the post he or she has just submitted
- only the person that has just paid to submit the post can see the post

I've got all this working except for the third step. I know how to make the third step work with a change to the functions file which automatically sets posts submitted through the form to private, but for the person who entered the post to be able to see it, he or she needs to be a logged in user/member. I can make that happen with a membership plugin but it occurred to me last night that there might be another way, by which I wouldn't need to worry about creating users/members.

The idea I have is this: if possible, I'd like to be able to:
- add a bit of code to the functions file which makes post entries through a specific form password-protected posts;
- add a single line text field to the form which asks the user to enter a password for the post
- somehow link the password that goes into that text field as the password WordPress requires for access to the submitted post

Is that possible please? If so, can anyone help please with the code that would be required for the functions.php file?

Many thanks in advance for any help.

Best regards
Richard

Absolutely superb. Thanks so much David. I'm so impressed with the GF crew, that I'm off to Tweet! @richard_best

Okie dokie. Did some more testing and the snippet I shared with you definitely works; however... WordPress handles post passwords in an odd way that may be causing some confusion.

When a user enters a password for a post, it stores that password as a PHP cookie. The problem is, it uses that same cookie for all other password protected posts on the site as well. This means that if more than one post have the same password, any user who enters the password for one will have access to view all posts with that same password without being prompted to reenter the password.

Is this what you are experiencing or are your posts not being password protected at all?

That would be helpful Richard: david@rocketgenius.com. Thanks!

Many thanks David. Much appreciated. I've tried the revised code but cannot get it working. Presumably I change the number in "gform_post_data_4" to the ID of my form (i.e., 1) and the number in "$post_data['post_password'] = $entry['6']" to the ID no. of the field into which the password is being entered (i.e., 63). I've tried this but the posts are still not being set as password protected. The full code I'm using in my relevant functions file is:

add_filter("gform_post_data_1", "set_post_password");
function set_post_password($post_data){

    $entry = RGFormsModel::get_lead($_POST["invoice"]);

    $post_data["post_password"] = $entry["63"];

    return $post_data;
}

(As you can see, I tried double as opposed to single quotes to see if that made any difference; as expected, it didn't.)

Sorry to keep bothering you with this. I much appreciate your help.

Best
Richard

That's perfect. Thanks so much David and Alex.

Just one final question please if I may: If I wanted to do the same thing for a number of forms on the same site, would it be OK to replicate the code a number of times, but adding the different form IDs and password field IDs, or would it be necessary to modify the code (into an array perhaps)?

Thanks again
Richard