This is fairly overdue, but MidMUD now supports login via Grapevine. You can’t connect your current account to your Grapevine account yet, but you can register a new account via Grapevine’s OAuth.
This gives a single sign on system for MidMUD. Once you have a Grapevine account you can also register your local character to your remote profile. In the future achievements (coming sometime!) and other pieces of information can be synced to your central account. This will be shared with any other games you sign in via Grapevine, which is a growing number of other ExVenture games!