Hi Sandeep,

It is not very secure to pass user credentials via querystring, so I suspect you will find little assistance along this avenue.  While HTTPS will prevent interception of such a querystring value, the user's credentials would be stored on server logs, possibly in browser history, etc.  Although it's an easy way to allow cross-application authentication, it's not a good one.  Avoid it.

You did say that your querystring was "posted (not visible in url)" so it's possible that you meant that you POSTed hidden form values.  Querystring values are not part of the form post process.  If that's indeed what you meant, then you are perhaps on a better track. 

You might be able to construct a hodge-podge cross-application authentication system in this manner.  To get the necessary control IDs which you will post to, I'd load up a dev toolbar like the IE Developer Toolbar (or the Firefox equivelent) and visit my DNN login page.  Click on the input fields and retrieve the name values of the input fields, and use these as names in your posting application.  This just might work.

However, it will be a pretty brittle solution.  When skin or container is changed, the values of these names could change as well, breaking your application.  There is no guarantee that DNN will not modify the authentication control hierarchy, also resulting in an ID change.

If you are trying to coordinate authentication across two applications, as it appears that you are, I would suggest (if possible) taking a step back and thinking about a more robust solution.  In DNN, this would likely involve a hybrid membership provider and some webservice hooks for the foreign application to access.  Note that these are reasonably advanced developer tasks (perhaps 6 out of 10 on the difficulty meter?).

Hope this gets you started!

Brandon