For no Ruby, this is a great PR. There are a few improvements you can make though. They aren't required but I think they'd be helpful.

If you use `required_config_value` ([doc](https://github.com/github/github-services/blob/master/lib/service/http_helper.rb#L33-L39)), it will raise an error if the configuration value isn't set but it also `strip`s it.

One way to take advantage of that is to change your `user_uuid` & `api_token` methods to look like:

```
def api_token
  required_config_value("api_token")
end
```

With the `required_config_value`, it will strip it, ensure it's not empty, and then return the value. If it is empty, it'll raise an error we can expose to the end user.