ASP.NET Forms Authentication with ADFS authentication?

I have a asp.net web forms authentication based application. it takes the user supplied credentials and authenticates them with an Active Directory class library to authenticate the user. I want it to instead verify the user credentials with ADFS (We now have setup an ADFS 3.0 server) in the code behind for authentication after they login via the application's login page.

Additionally, when the user first hits the application I want to check ADFS first to see if the user is already authenticated with ADFS or not. If they are then it goes directly into the application bypassing the login form. How can I achieve this?

The current examples I've seen set things up where it takes the user to a login page on the ADFS server itself if the user is not already authenticated. I don't want them to have to hit this "global" ADFS login page on the ADFS server and instead keep using the application's local login page.

basically I want: 1) authenticate using ADFS and 2) use my application's login form and not the ADFS login page.

any help is appreciated.