Hi Garry Clark,
Thank you for using our servicves.
I can suggest that you take a look at the following articles explaining how to achieve Single sing-on with Forms Authentication. As Sitefinity uses Forms Authentication you will be able to achieve it with the CMS:
Single sign-on with Forms Authentication
Single Sign-On Across .Net Web Apps Using Forms Based Authentication
I believe that you would also be able to integrate your Help Desk as a module in Sitefinity. As long as it uses the Provider Model and has an API you will be able to wrap it up as a module in the system.
I hope that our comminity members will be able to suggest some help desk solutions and tell their experience with them.
the Telerik team
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