For authorization, a forum account in good standing above a certain trust level might be used. Or if processed through a moderation queue, perhaps any DC account via QR sign-in could be allowed. The commenter should not be required to hold a GitHub account.
The scope could be greatly extended with various features (searching for and following issues, sending patches, hooking this up to a bug report button in the DC client itself, etc.), but this alone would cover the most dire use cases that really make an impact.