easy - return a response header.js

fetch(url, {opts})
  .then(response => response.headers.get(`Authorization`))

easy: return parsed json.js

fetch(url, {opts})
  .then(response => response.json())

hard - return updated auth token + parsed json.js

// {}.data is a promise, not the parsed json
fetch(url, {opts})
  .then(response => {
    return {
      authToken: response.headers.get(`Authorization`),
      data: response.json(),
    }
  }

// response is already consumed and parsed, response.headers is now undefined
fetch(url, {opts})
  .then(response => response.json())
  .then(response => {
    return {
      authToken: response.headers.get(`Authorization`),
      data: response,
    }
  }