Dealing with Oauth 2.0-facebook gem error 100: This authorization code has been used

Question

I have been working on setting up facebook authentication for my rails app and while testing, after logging-in with my facebook account, I keep getting this error:

Answer 1

I was incorrectly initializing OmniAuth twice, calling config/initializers/omniauth.rb twice.

This would add OmniAuth::Builder twice to the middleware stack. With recent Facebook changes, this started failing with error 100.

Making sure OmniAuth::Builder got added once I managed to solve this issue.

To double check your middleware stack, run this:

rake middleware