<p>I have a form that sits behind ASP.NET forms authentication.  So far, the implementation follows a typical "out of the box" type configuration.</p>

<p>One page allows users to post messages.  If the user sits on that page for a long time to compose the message, it may run past the auth session expiration.  In that case, the post does not get recorded... they are just redirected to the login page.</p>

<p>What approach should I take to prevent the frustrating event of a long message being lost?  </p>

<p>Obviously I could just make the auth session really long, but there are other factors in the system which discourage that approach.  <strong>Is there a way I could make an exception for this particular page so that it will never redirect to the Login so long as its a postback?</strong></p>

My coworker came up with a general solution to this kind of problem using an HttpModule.
Keep in mind he decided to to handle his own authentication in this particular application.
Here goes:
He created an HttpModule that detected when a user was no longer logged in. If the user was no longer logged in he took the ViewState of that page along with all the form variables and stored it into a collection. After that the user gets redirected to the login page with the form variables of the previous page and the ViewState information encoded in a hidden field.
After the user successfully reauthenticates, there is a check for the hidden field. If that hidden field is available, a HTML form is populated with the old post's form variables and viewstate. Javascript was then used auto submit this form to the server.