decioferreira/omniauth-linkedin-oauth2 — pull request #1 by emorikawa (2013-07-30 21:48:18+00:00)
Title: URGENT Site Endpoint Incorrect - LinkedIn Omniauth Broken for All Heroku Users

http://developer.linkedin.com/comment/26121#comment-26121

Over the past 4 days, no one running this gem on Heroku has been able to get access tokens from LinkedIn!!
It seems the fix was changing the site uri option.

Please read the full discussion thread above.