Sorry @pfaffman, but I’m afraid I will have to remove this new rake task in an upcoming PR. We are going to be hashing API keys in the database, so it will be fundamentally impossible to retrieve an existing key.
https://github.com/discourse/discourse/pull/8438
I’ve replaced the get_or_create_master task with a simpler create_master task, which will unconditionally create a new key. If you want to only have one key, then you will need to keep track of the key in your own system.