Manage Access to Yale Netids at SalesForce

First, Setup SSO, look here.

Under Administrative Setup -> Manage Users -> Users

Use the UI to create a user that you want to access the site.

Fill in all the information you have to the user. To allow federated SSO, which you do, navigate down to Single Sign On Information, and enter the users netid in the Federated ID field.

And that is it. You have CAS protected your SalesForce Site via SAML2.0, enjoy.