Facebook Login Error: CSRF detected


My users cannot log in with Facebook anymore. This is the error log:

(facebook) Authentication failure! csrf_detected: OmniAuth::Strategies::OAuth2::CallbackError, csrf_detected | CSRF detected

I’m using Cloudflare in front of nginx. I’m using Cloudflare automatic SSL (flexible). I didn’t install any certificate on my server (i.e. I’m not using Letsencrypt).

Is this related to Cloudflare? Can this be solved without installing Letsencrypt?


This error is similar both for Google and Facebook. In my configuration there was a line in nginx:

# proxy_set_header X-Forwarded-Proto $https;

After I changed it to

proxy_set_header X-Forwarded-Proto $scheme;

the error has gone.

Solution was found after reading this topic: Redirect URI mismatch in Google Auth