Custom Security Extensions for SQL Server 2008 R2 Reporting (SSRS) - "Temporary User issue" by Har P

We are using Custom Security extension for user authentication (form based) for SSRS reporting access, we are getting an error

"The remote server returned an error: (500) Internal Server Error." for the first time click from web based application or even if access directly the report manager, for the second time click the report page gets loaded. When i tried to log the custom security extension code, on the first click we are getting "Temporary User" in GetUserInfo() method, so as its not a valid user to get the access we get http 500 error on the screen. This happens when we restart the Reporting Services and click on any of the reports in Report manager for the first time, but it works on the second click.

Have tested with many scenarios by tweaking the custom code and also logging the errors to trace the issue, but we get "Unknown" or "Temporary User" on the first click inside GetUserInfo() method. On the second click we get access to the reporting services which is strange.

How to handle temporary user in custom security extension code so that we can avoid the Http 500 error before it loads with proper sign on user. As per the analysis made, the issue is with Microsoft Product (SSRS), once the temporary user is created as per the CU3 release from Microsoft, but its not handled to check the proper user authentication until its found.

It seems Microsoft Product issue, any fix/resolution from Microsoft much appreciated.