My application needs to pay some users regularly and automatically via PayPal.
I'm planning to do this using Adaptive Payments APIs. To use the API I need to know the user's PayPal account.
Of course I can simply ask the user for his account name, but without validation it's quite possible that he will make a typo or some other mistake and his money will end up in someone else's account.
So, I'd like - ideally - for the user to go to PayPal, authorize there, and let PayPal return me his authenticated account ID.
How can I do that?