You need to authenticate your communication with the ClearML server initially somehow, no? Otherwise basically anyone can create credentials on your server...
After you have authentication you can create credentials via the terminal.

You can create up to 10 sets of credentials per user so if you plan on creating new credentials every time you want to run a job - this is an incorrect approach.

Therefor - you should create the credentials once and then use them as environment variables as you were suggested to do.

Makes sense?