Comment 2 for bug 449708

Original notes from marketo prototype for reference:

Find a way to make SSO less intrusive. For optional login, we'd like to be able to check if the user is logged in and auto-fill the form with their SSO data if they are, but not stay on SSO to request login if they aren't. The best way I can think of doing this, with an eye on future improvements, is to implement check_immediate in SSO. This should be simple enough to prototype using the standard python-openid libs as we won't need any restrictions for use of the feature, but we will need to carefully review how we implement it before we commit it to trunk/production.