Q:

C#, .Net - Implementing Forms Authentication using a custom user validation

Basically I have a web app that I'm building on top of an existing API and when the user logs in the userName and Password are passed via a SOAP call for authentication and I get a response telling me if the user is valid or not along with a status code (and other info).
But that's pretty much it. I'd like to implement basic Forms Authentication that uses this API call to validate the user and essentially log him in to my web app. Right now we only have to worry about one role, so everybody that logs in sees the same thing.
I'm not quite sure where to begin...

A:

Implementing a custom membership provider is fairly simple: see here: http://msdn.microsoft.com/en-us/library/f1kyba5e.aspx for details.
You should be able to combine this with WCF to get what you need. 
For the methods that aren't appropriate, e.g. changing passwords, then throwing NotImplementedException is the right thing to do.

