We just started using Gerrit, but using Github authentication. Can't sign in! Not doing our own account management appears to have been a poor decision.
Every time a service like Github goes down, I always swear to myself I'll replace that dependency with a project that takes days, weeks, or months to implement will ensure I'll never have hours or minutes of downtime ever again.
I run a gogs[0] instance, which is a GitHub clone with great performance characteristics. I use it for both company and personal projects, and we haven't had any downtime. No more productivity drop when github is down :D.
I recently discovered another huge dependency I have when coding though : StackOverflow. That's going to be a lot harder to replace though...
It could have been the motto of RhodeCode (https://rhodecode.com). Self-hosted repository management not only has a benefit of having one's uptime under control, but also is much more secure.
This isn't an argument against third-party account management. It's an argument against single points of failure.
You can (and many websites which do) support multiple auth providers such as Facebook, Twitter, GitHub etc. If you bind your account to multiple of these providers, you can mitigate this risk to a large extent.
Even with that setup, people normally don't bother to associate more than one set of credentials with their account. So you would have to institute a more-than-one credential practice.