What is the simplest way to consume an external REST service in Lagom?

A way to consume 3rd party REST services from lagom is by writing the 3rd party's REST spec using a Lagom Descriptor.

Imagine your code wanted to interact with Slack's API, you would create a slack-api project in your app and create the Slack descriptor there (you wouldn't need to create a slack-implof course).

Then, on your fancy-impl code you would depend on slack-api and in your FancyServiceImpl implementation you would inject SlackService in the constructor.

PS: The gist is scala code, but same idea applies to Lagom's Java DSL.