Pass login credential from another site

My requirement is that when logged in users from a another .net website come to access the WP site where my forum is hosted, need to send UN and Password from that site to my WP site – thereby requiring no login at my WP site. Is this possible? pl. let me know the way to do this. Thanks.

Note: Users are imported from the another .net website to the WP site using Members Import plugin thru CSV thus have the same uname and pwd for both.