The phrase "missing authentication token" is historic and is based
around the use of "AuthenticationToken" objects inside the Realm code.
However, now that we have a TokenService and token API, this message
would sometimes lead people in the wrong direction and they would try
and generate a "token" for authentication purposes when they would
typically just need a username:password Basic Auth header.
This change replaces the word "token" with "credentials".
e16fd4ebd6