Form validation woes/answers.

Hi all--
Muscled through this bear of an issue and wanted to share my story.

Building an ubercart site, and need to customize the /cart/checkout page to allow a user to log in from there.

Used hook_form_alter to add the necessary fields and a custom submit button. Added my own validation function, and inserted it before the ubercart validation function:

Issue I was running into is that there are a bunch of #required fields in this form. It is a little taxing programatically to remove the #required tag from all of Ubercart's fields because they're buried very deep in the form's structure, so I found a better approach that works great.

Note:
My validate function only happens if someone clicks my login link-- you wouldn't want to follow my approach for a general case validation function.

The reason this was necessary is that I was using user_authenticate() to actually attempt the login, which checks for form_set_errors() before approving the login, so I had to clear out any errors from the #required form elements otherwise user_authenticate would never work.

Anyhoo, that's my bit of knowledge for the night. Let me know if you have any questions.

If nested forms were a possibility, that would be a better way to go, but we gotta work with what we got.... :)