.net - Fine Tune A Membership Provider?

After all the answers to my last question about fine-tuning turned out to be more useful than I expected, I thought that I would ask another similar Question about the MembershipProviders as well.

Okay, so firstly, to clarify: I know what a Membership, Role, and Profile provider is, how to implement my own, and how to configure them, and most of the things about them. Implementing a role and profile provider is pretty straightforward, because they only require simple CRUD most of the time. (A single line of LINQ is enough for about half of the RoleProvider's methods.)

However, the Membership provider is a differend beast. Many of you may realize that it violates the SR (Single Responsibility) principle, because it has to do EVERYTHING related to user management. While this leaves a lot of room for customizations, it has its downsides as well. There is no information on the Internet about what their EXACT expected behaviour is, such as when should they throw exceptions or simply return null, and stuff like that.

I use this sample implementation for reference, but it also contains several contradictions.

For example, it uses its own ValidateUser method for checking for credentials in the ChangePassword method. But the ValidateUser also updates the user's LastLoginDate to the current date. So, does the framework expect that I set it in my own provider as well, or is it simply a mistake in the sample? The other is: the ChangePassword method throws an exception every time when validating the new password, but CreateUser doesn't ever throw an exception, it simply returns false. And last, but not least: it counts the invalid password attempts of the user and locks them if it passes a threshold. While this is good, but it requires manual action to unlock the users. Is it a problem if my provider automatically unlocks the user after a certain amount of time? (EDIT) I almost forgot: the CreateUser method in the sample inserts the ID from the method parameter. I actually think this is bad practice, because I use inters with auto incement as IDs, so inserting them from some method parameter is not an option. Should I just ignore the parameter, or require that its value is null and throw an exception if it isn't?

All in all, does ASP.NET have any assumptions about the behaviour of a MembershipProvider? Is there any documentation which describes when should I throw an exception or just return null?

I also tried to find a set of generic unit tests which would provide some guidance about the expected behaviour, but no luck, I found plenty of articles about "Unit testing is good", and "How to unit test a MembershipProvider", but not one where there would be any actual tests.