This is actually a pain point our company (https://www.dailycred.com https://www.dailycred.com) solves. If a user forgets the method they used to sign up, we'l

This is actually a pain point our company (https://www.dailycred.com https://www.dailycred.com) solves. If a user forgets the method they used to sign up, we'll still return the right user record to your app. Be careful implementing this, because it can be a security issue if you're not cautious.