How can i use custom forms authentication or forms authentication with 3 fields in my web application

Question

Hi all,

            I am developing a web application , which have the log in page with 3 fields(company id, user id & password).

I saw some articles in in the internet for forms authentication , but those articles explaining with user id and password only.

So please tell me or guide or share some links how to use forms authentication with 3 fields.

Thanks