Before using Monkey Farm, you need an account. You can register via the web interface, or more easily by the command line utility.
$ mf user register
Note that, you are prompted to provide an email verification code. This can be safely terminated as the email sent also provides a clickable link to verify the email address. That said, take note of the api key provided. This is an autogenerated api key unique for your user. Copy the key to the ‘api_key’ setting in ~/.mf.conf.