OWA 2013 custom authentication to /owaauth.dll

Hi,

We have enabled Forms Based Authentication for OWA 2013 and POST the data [user credentials collected from our custom login form] to "https://{hostname}/owa/auth/owaauth.dll".

In earlier versions of OWA [2007 and 2010] it works fine.

But, when we have installed OWA 2013, the authentication fails with an exception "Object reference not set to an instance of an object...".

Our PostData looks like:

"destination=https://{hostname}/owa&username=domain\userid&password=password&SubmitCreds=Log+On&forcedownlevel=0&trusted=0&flags=0";

In addition to this we set 'UserAgent' and 'AllowAutoRedirect' for the 'HttpWebRequest' object.

Are we missing any parameter here or does OWA 2013 needs any additional information for a successful authentication.

Thanks in advance.

Regards,

Madhu Gowda