CYB-61: add Ruby auth client

An auth client isn't just used once to get a token, but each time you want to use the token, you should do authClient.getToken(), since it automatically refetches if the cached token has expired.
For the use case that you need to connect to another cluster and get a token from it, you should use an altogether different instance of the AuthClient, so you can make requests to both clusters (and each client will be responsible for refreshing their respective tokens).