Okay, using the above information I was able to connect Social to FB and Twitter after I contacted Hostgator and had the rule whitelisted. That works.
What isn't working is when a reader tries to click on "Sign in with [Twitter or Facebook]." Rather than sign in, the pop-up window simply displays my home page with this URI:
http://www.mydomain.com/?social_controller=auth&social_action=authorize&target=https%3A%2F%2Fsopresto.mailchimp.com%2Ftwitter%2Fauthorize&post_id=1791
I'll try talking to HostGator again about this, but has anyone experienced this separate-but-possibly-related issue? If so, was it a different mod_sec rule?
Thanks,
H.