Sure, validating a user is actually super easy. Just download your whole DNN site and db and get it running locally. Then, open it with VS and follow this tutorial
http://www.dnnsoftware.com/communit...PI-Edition Once you get the hello world app working, just drop this function in and then call it via yourdomain.com//DesktopModules/MyServices/API/Welcome/ValidateUser?username=someUser&password=somePass
[AllowAnonymous]
[HttpGet]
public string ValidateUser(string username, string password)
{
return System.Web.Security.Membership.ValidateUser(username, password).ToString();
}
You'll probably want to secure that over ssl, and have a key that you're passing as well. You could also pass in json or post data as well. Just change the HttpGet to HttpPost or whatever method you want to use. That will return true if it's a valid user, and false if it's not.
Let me know if you need help getting the DNN web services thing created.