I would like to keep track of the App Usage to not exceed the API rate limit. The response headers are lost in the module and it would be great if there we're a function to check what the current usage is.

A quick work around could be to just add in the data in the response if it's set.

if (res.headers.hasOwnProperty('x-app-usage')) {
      body = body.replace(/\}$/,',"appusage": ' + res.headers['x-app-usage'] + '}')  
    }