Facebook OAuth2 with DotNetOpenAuth under MVC3

Question

I'm trying to authenticate on FB (and Twitter, also) using OAuth. Looking at the 3.5 CTP for DNOA, I was able to get the ASP.NET sample working.

But I'm lost about how to convert it to work in MVC3.

I tried the naïve approach and moved the sample code from FacebookClient.cs into a small assembly that I call from a controller action, but it dies here:

client.RequestUserAuthorization();

due to the fact that the HTTP headers have already been returned and cannot be re-written.

So I tried modifying this call to return an action result:

return client.PrepareRequestUserAuthorization().AsActionResult();

But this fails as it forces the browser to try and download something from facebook.

Does anybody have any advice on how I can get my MVC3 app to authenticate against facebook? I really wish DotNetOpenAuth's CTP included an MVC sample of OAuth2 authentication; I see a LOT of people banging their head against this. Andrew, save us!

Answer 1

Hmmm... things seemt to be working better now, using this:

fbClient.PrepareRequestUserAuthorization().Send();

It seems like FB may have been tweaking things on their end, but I am not sure.