how to match facebook login credentials with registration details in our database?

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C#

ASP.NET

Hi,

I am just confused as we have a registration page of our website where visitor completes the form and we save his registration details in our database and whenever he ask questions or give comments or answers on our website then we can save all this in to our database. But if we allow visitor to login by facebook, then how will we maintain or save his question answers and comments into our database as our website's user?

The more of the problem is when :

(1) we allow a visitor to create an account with our registration form and he enters his e mail id as log in id for logging into our website account and suppose if he uses a different e mail id for his facebook account later to log in to our website, then which of the IDs will be matched with our database.

(2) Secondly, however he is allowed to log in our website with his facebook account how his question and answers or comments will be saved in our database if he enters with facbook id because he will get through the log in our website but his login credentials will not match with our database. and we want his QnA or comments to save in the same account with which he registered with our website.

(3) Thirdly, I know there is an option where we can also ask visitor to register with facebook account but in that case I think the data will be saved in facebook database and we will not be able to save the info in our database. please correct me if I am wrong.

In short, it may be login with facebook or login with gmail; my point is that how we will save all the info in our database.


I request you to answer me this question in point to point style. And share your views and suggestions.

Thanks in advance.