How to custom credential provider

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C++

Good day all

I am trying to add another field to a membership provider on login the user will receive a email
with a code which he then has to enter on the login screen only then does he get logged in. I know c# but my experience with c++ is null to say the least. I have downloaded the samples from msdnand read trough the directions the problem is I still don't understand how to add a field to the credential provider and do verification before login the user in.

I am just looking for someone who has done this before to give me some guidelines any help would be appreciated