Article ID: 2592933 - View products that this article applies to.
A Microsoft Forefront Threat Management Gateway (TMG) 2010 Forms-based authentication cookie is only valid on the array member that generated the cookie.
If a client request that contains an authentication cookie from one array member is sent to a different array member, the client is asked to reauthenticate. This behavior may occur when a node is taken offline. Or, this behavior may occur if the client source IP changes between requests that affect which array member handles the incoming request. The Client IP address can change during a browsing session when clients access the Internet on a 3G connection.
TMG uses a set of server-specific encryption keys to generate the Forms-based authentication cookie. These keys change periodically and are not shared between array members. Therefore, an authentication cookie that one array member issues cannot be used on another array member.
TMG Service Pack 2 adds functionality to support cookie sharing across array members. To do this, TMG Service Pack 2 enables support for the cookie encryption keys to be shared across array members. To support sharing cookie encryption keys, the array members must be domain-joined. Be aware that this does not work for workgroup-based array members.
To resolve this problem, install the service pack that is described in the following Microsoft Knowledge Base article:
2555840To enable Forms-based authentication cookie sharing across array members, follow these steps after you install TMG Service Pack 2:
(https://support.microsoft.com/kb/2555840/ )Description of Service Pack 2 for Microsoft Forefront Threat Management Gateway 2010
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
As noted earlier, for the cookie sharing to work, the TMG Array members must be domain-joined. This condition is required to support the sharing of cookie encryption keys between array members.
You should be aware that the Published server logoff URL functionality does not work across array members. For the Published server logoff URL functionality to work, a specific application URL is configured as the logoff URL. When the user requests this URL, the TMG server moves the user cookie into a tombstone list. Therefore, if a client re-presents the URL, the URL is interpreted as invalid.
This new functionality does not allow for the tombstone list to be shared across array members. After the logoff URL is used, an array member can accept a cookie. Then, the cookie moves to the tombstone list on a different array member.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
(https://support.microsoft.com/kb/824684/ )Description of the standard terminology that is used to describe Microsoft software updates
Article ID: 2592933 - Last Review: October 31, 2011 - Revision: 2.0