David Recordon wrote:

I assume having read the various responses that what we're discussing here is selecting the RP selecting different provider if the the RP is an explicitly-mobile site, such as http://m.facebook.com/.

Now that I understand what you're trying to achieve, I can get behind it a bit more. I'm still not completely convinced that it's going to be that useful in practice, though: I know I generally use the main "desktop" version of most sites I visit on my phone, just because they tend to be more complete. I'd still prefer to see the a mobile-friendly OP UI, though.

Also, some sites will have their main site simultaneously be the mobile site by simply providing a mobile stylesheet and doing capability determinations in script on the client-side. Such sites would have no reliable way to determine whether to set this flag or not, and would presumably therefore always use the non-mobile version.

Finally, I'd be curious to hear which OpenID providers you percieve to have poor mobile experiences and what in particular makes them poor.

I think I'd prefer something that requires less disruptive changes to what an RP is expected to do, such as something similar to the language preference proposal where the RP sets a flag saying that it's a mobile site in the request which allows the OP to select a mobile-friendly UI if available. This gives the OP an opportunity to make the switch if necessary, and can be implemented as a standard OpenID Auth extension.

If a provider depends on some specific hardware to do authentication, then it's the responsibility of that provider to come up with an acceptable solution for situations where the user is unable to use that hardware for whatever reason.