Drupal single sign-on across domains

Question

I'm trying to integrate two sites (one is drupal-based, the other isn't) using a single sign-on. Our client uses drupal (developer/API site), and would like users to be able to login to our site (developer contest, different domain) using their credentials.

I've explored OpenID, and I don't believe OAuth is appropriate for this kind of thing, though I could be wrong.

Would it be easier to just build our site in drupal and work out some kind of multi-site solution? Really I'm looking for a simple way to authenticate a user and avoid having them create a separate account to login to our site. Ideally a user would come to our site, enter their credentials, which would then be checked against the drupal database on our client's site, then they'd be passed back to us. This is as far as authentication needs to go, the point is to be able to read a drupal user database and verify an account exists. Users will not need be registering on our site, only logging in IF they have a developer account on our client's site.

Answer 1

There are many different single sign-on (SSO) modules that might be helpful starting points; for a more-or-less complete list, see this Drupal Groups page. From my research, OpenID appears to be one of the more robust solutions; the flexibility to set up your own identity provider or use an existing system (there are many) seems like it would be valuable. Considering the age of this post, I'd be interested to hear the direction you went and your experience.