How would you allow a user to authenticate and post a comment at the same time

I'm looking to implement a similar feature to DISQUS for my app where a user can post a comment and login to my site at the same time.

The way I see this working is the user is shown a text field for th开发者_运维知识库eir comment along with a submit button. When the submit button is pressed then the user will be shown a variety of authentication providers (facebook, twitter etc) and after authentication is complete the comment is posted.

I already have commenting and authenticating working as two separate actions but I'm wondering what the best solution is to combine them into one.

You could also use a modular popup for authentication instead of redirecting to a new page. Another option would be to have a drop-down button as the submit button with options like "Post with Facebook", "Post using my Twitter Account"...