I'm guessing you will have to create your own membership and role provider. (Or google to find someone who has allready created an ClearTrust provider)
Read more about providers here:http://sdk.episerver.com/library/CMS5/Developers%20Guide/Membership%20and%20Role%20Providers.htm?id=24871
We did not build any special RSA ClearTrust-support in EPiServer CMS 5. If it says so on our sites somewhere we will need to adjust this.
When building version 5 we decided to use the standard .NET Provider model which should mostly eliminate the need to do anything special for EPiServer to get SSO to work. Very few have also asked for it so we have not put it in the product backlog. If it is a need to do a more EPiServer-specific implementation, we will though add it as a new request.
We are sorry for the confusion around this and we will try to adjust the material on our web sites.
Roger WirzProduct Manager