Suppose there are 2 web site:
example.com I don't own and
example2.com I own. I want to extend the functionality of
example.com doesn't have any API. I want the users of
example.com to be able to login at
example2.com using their logins and passwords of
example.com. However, since
example.com doesn't have any API, it is not easy to do, perhaps, it is even impossible.
No doubt, no one would agree to enter their credentials of
example2.com due to many obvious reasons.
So, is there any way to authenticate the users of
example2.com (or somewhere else) using their original credentials?