AD authentication online for multiple organizations

Question

what is the best way to bring Active Directory Authentication of two (or more) Organization online for a single web application ?

we are working on web application that will be used by more than 1 organization but all the organizations need their employees be able to access the web application using their own active directory usernames and passwords (again AD of each org is privet to it only )

is this even possible

Answer 1

Windows Identity Foundation maybe? WIF description

Answer 2

You could use Federation for this. Federation means that you leave the authentication responsibility to the federated domain, you only setup a trust relationship to this domain so that you accept it's authenticated users.

One of the possibilities is to adopt Claims Based Identity ( http://en.wikipedia.org/wiki/Claims-based_identity ). In this case you might want to take a look at Windows Identity Foundation ( http://msdn.microsoft.com/en-us/security/aa570351 )