I'm looking for an extensible implementation of a dual purpose login/signup form, written for MSofts MVC3.

It's a bit tricky, since the two have different validation requirements.

Some details in response to comments:

* Dual purpose as in, the form should be able to serve for both sign-in and sign-up purposes.
* The trickiest part is probably the validation, and I would be surprised if a solution doesn't use custom validation code to work properly
* Extensible so I can use my own fields rather than some hard coded fixed ones. I've found some solutions where extending them was the same order of magnitude of effort as starting from scratch