To manage a successful login to the Out look Web Access it's done thru the owaauth.dll on the outlook exchange server. You simply need to pass "the correct parameters", it took me a while to figure this out!!
Anyhow the owaauth.dll requires mainly those parameters:
Send a request with the destination, username and password. It's based on FBA(Form Based Authentication) , i.e: a POST is required
-Add the parameters to ur request body
-The Response object on a valid user login contains two cookies: (sessionid, cadata). So ur main check for a successful login can be the returned Cookies Count (Response.Cookies.Count > 2)
If your exchange mail server under SSL don't forget to use "https://" in ur exchanger server URL.
On LogOff, clear any cached credintials use this client side script:
document.execCommand("ClearAuthenticationCache",false);
The following article helped much:
http://www.infinitec.de/articles/exchange/webdavwithfba.aspx