Using Single Sign On to log into external website from SharePoint

Question

We have a SharePoint 2010 server and another site (a service desk tool) that has a custom forms based authentication (not related to SharePoint).

It would be nice if the SharePoint users wouldn't have to login into the external system again. If they are logged in with SharePoint and click a link inside SharePoint to the external side (or maybe the site could be displayed inside an iframe inside SharePoint) they should be logged into the external site straight away.

I don't have that much knowledge about SSS but had a look at it and I think that maybe that isn't really that what could be helping me. Also I'm not sure if this is this is technically possible without modifying (adding code) to the external site.

Somehow the external site should see that user XY arrives and look into the SSS I suppose to find the corresponding user and use that login information to authenticate the user. Can it be that I understand SSS wrong?

What would be an approach to this issue and is there one that can be done with SharePoint Out of the Box tools (without programming)?

Answer 1

Apparently, I did understood it wrong. We now try to solve it without the use of SSS but instead storing the data in a sharepoint list and some code that tries to match the logged on user with the list data and then opens up the target site with the corresponding parameters.