When we evaluate features for any of products, we try to find a balance between DotNetNuke functionality, third-party offerings and overall value. This is one of those areas where I find it difficult to expand into Active Social when there are already other solutions available. However, I do think it is our job to make sure we provide solutions that cater to community needs and usability. The fact that we haven't implemented this request yet doesn't mean we don't care, it means that we don't have the ideal solution yet

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Now, this isn't just about authentication. This is about authentication and registration. In most cases, a typical DNN site provides separate links for Login and Register. This immediately creates a usability question for new users. This usability problem also will create user account issues further down the road. Let's walkthrough the process as a new user.
1) I visit your site and I want to join.
2) I click register and sign-up.
3) When I return to the site I click Login.
4) I see I can enter my username and password or use Facebook.
5) I choose Facebook.
6) Since I really don't know how the site works, I just created a new account using my Facebook information that isn't associated with the account I created previously.
See the problem? Now, there are ways to associate that old account with the Facebook account but that really isn't user friendly either.
How could we make it better?
1) I visit your site and I want to join.
2) I click register and see the sign-up along with a button that says I can sign-in with facebook.
3) I click the facebook button and authenticate.
4) I'm now presented with the site's edit profile page which is pre-populated with my facebook data.
5) I can change or enter data that is necessary to complete the registration process.
6) When I return to the site I click Login.
7) I choose the facebook login button and I'm ready to go.
Now, while that might sound pretty easy, there is a lot that needs to be considered behind the scenes. To be perfectly honest, while this is definitely a benefit to community sites, it really needs to be addressed at the DotNetNuke Core level. In my opinion, if third-party modules need to "hack" the DNN registration process to be more user friendly then DotNetNuke needs to make some changes. This is an area of DNN that hasn't really made any progress since DNN 3. Instead of adding this functionality to Active Social, I think I will write up a recommendation and code package for core submission.