In Windows Server 2008 R2, the Web Single Sign-On (Web SSO) feature provides users with the ability to enter their credentials only once during logon to Remote Desktop Web Access (RD Web Access). After logon, users can launch RemoteApp programs that’re part of the same connection in RemoteApp and Desktop Connections without any further credential prompts, even if the RemoteApp programs are configured to use RD Gateway. Why is Web SSO necessary? In Windows Server 2008 TS Web Access, a major pain point for users was receiving multiple credential prompts, first when logging on to TS Web Access and then when launching a RemoteApp program from a terminal server. In Windows Server 2008 R2, using the new RD Web Access Forms Based Authentication (FBA), users’ll now’ve to enter credentials only once in the login page of RD Web Access and’ll not be prompted again for entering credentials on launching subsequent apps from the RemoteApp Programs page of RD Web Access.
Full Article: RDS blog