How to assert that the response contains a key, e.g. "authToken"?

We can do things like:

assert.equal(body.json.widgetType, 'gear', 'Expected a gear widget type');

and

const info = JSON.parse(body);
     console.log(info.stargazers_count + " Stars");

But how do we assert that the body json contains a key of “authToken” with any value?