Consider the following scenario:
You publish an Outlook Web Access (OWA) website by using Microsoft Forefront Threat Management Gateway (TMG) 2010.
The website uses RSA authentication.
You authenticate a client connection by using OWA Forms Based Authentication (FBA).
You enable an idle time-out setting for Public Computers and set a specific time.
You enable the No delegation, and client cannot authenticate directly setting or the No delegation, but client may authenticate directly delegation setting.
You connect to the OWA website from a public computer and wait some time before you continue to use the website.
In this scenario, you may be prompted for your credentials unexpectedly while you use the OWA website. This authentication prompt may occur periodically.
This issue occurs because the idle time-out setting for public computers is handled incorrectly as a session time-out.
When a public computer connects to the OWA website, you are prompted for credentials. However, the session times out after the time that is specified in the idle time-out setting. Therefore, authentication is required again while the connection remains active.
To resolve this problem, install the hotfix package that is described in the following Microsoft Knowledge Base article:
2735208 Rollup 3 for Forefront Threat Management Gateway (TMG) 2010 Service Pack 2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates