Single sign-on applications usually use an ISAPI Extension on Exchange servers in order to swap-out credentials being passed to OWA. This type of manipulation is not supported by Microsoft. In fact any thing which augments the behavior in this way is not supported. While such filters/extensions may have worked with Exchange 2000 and 2003, they are less likely to work with OWA from Exchange 2007. If you have a problem with such an Extension/Filter, please contact your software provider. It will be up to ther software provider to find their own solution on this as its not supported my Microsoft.
When we see developers's trying to use an IFRAME to hold OWA it almost always means their program is trying to use credentials collected from their own ASP page and pass them to OWA running in an IFRAME. The type of application is usually some sort of portal. They would try to use the credentials entered on the portal logon page (usually ASP forms based authentication page) with OWA. The two problems here are that the IFRAME does not share security contexts with the rest of the webpage, and the fact that you cannot directly give credentials to OWA to use. The way they try to get around this is by using an ISAPI extension which can use the credentials entered on their page and use them in a swap-out with the credentials that OWA uses in the HTTP traffic going to the OWA server.
An ISAPI extension is used by some developers. Such an ISAPI Extension would sit in front of OWA/DAV and change-out the credentials in the HTTP stream. This can cause many types of problems. It may work most of the time, however it may break WebDAV or OWA at different times – I’ve seen this happen several times. Note though, that ISAPI extensions are very much supported. I’ve never seen anything saying that there cannot be an ISAPI Extension sitting in front of OWA and just monitoring traffic. However, the fact is that doing such an operation on the OWA stream (changing credentials, etc) is not supported. Changing the stream of OWA amounts to hacking the application – which is not supported.
Microsoft does not support using ISAPI extensions or filters to modify Outlook Web Access credentials on a server that is running Exchange Server http://support.microsoft.com/kb/938609