Enable HTTPS-HTTP Bridging on the TS Gateway

Open TS Gateway Manager.

In the TS Gateway Manager console tree, right click to the TS Gateway server, click Properties.

On the SSL Bridging tab, select the Use HTTPS-HTTP bridging check box, click OK.

A warning message will appear, stating that for the SSL bridging settings to take effect, you must recycle the default application pool of IIS. If you want to recycle the default application pool now click Yes. To recycle the default application pool manually later, click No.

ISA Server Configuration for TS Gateway

http://technet.microsoft.com/en-us/library/cc731353.aspx