how to send and retrieve custom form info through paypal IPN?

It seems that Paypal limits what what information can be retrieved by the paypal IPN php file after the user pays. I want users to be able to make an username and password that they will use to log in to my website before they click the paypal checkout开发者_开发知识库 button. After they pay, my paypal IPN php file will retrieve their username and password and place them into my mysql database. Is this possible? I want to make registration as easy as possible for the users.

Thanks in advance

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there are a couple of custom fields that you can add to your form that paypal will return no matter what you sue them. however i would recommend saving the data locally, before sending the rest of to paypal, to do this you either nee to use AJAX to submit part of the form to a php script or pre-possessing the form data before sending to paypal via curl.