Connecting to MongoDB database on mLab fails authentication
As of March 2016, mLab.com only supports mongo 3.0+ (as per a conversation with support), because of their new onerous authentication requirements.
This was not on the website, but I hope it helps someone here!
You can get the dbuser and dbpass with:
heroku config | grep MONGODB_URI
Grab the dbuser (example_user) and dbpass (example_pass) from the response:
MONGOLAB_URI: mongodb://example_user:[email protected]:12345/db