Apollo-link: [Bug] apollo-link-context "setContext" not sending context

Intended outcome:
I'm trying to use the "setContext" function to set a token asynchronously.
I'm expecting to find the token set in"setContext" in the header of my request or somewhere else.

( See the code in how to reproduce the issue ).

Actual outcome:
The request never contains my token or any context I'm sending.
Not working in a synchronous way either.

this is the request I get :

{ data: {},\n context: \n { request: { sourceIp: '110.169.68.32', headers: {}, httpMethod: 'post' },\n auth: null,\n sessionCache: {},\n environment: {},\n graphcool: \n { rootToken: 'eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE1MTI5NzkxNzEsImlhdCI6MTUxMjk3ODg3MSwiY2xpZW50SWQiOiJfIiwicHJvamVjdElkIjoiY2o5dnAwMzloMTl2bjAxNDhlc3UzbnYzMSIsInBlcm1hbmVudEF1dGhUb2tlbklkIjoiY2piMXdrMHR2NGExNDAxNTRxMXBrMnh0diJ9.WcqQchOGD-BwwwM4Nmh0zYoOpPk7YcGk1qzRcutDxmY',\n endpoints: [Object],\n projectId: 'cj9vp039h19vn0148esu3nv31',\n alias: null,\n pat: 'eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE1MTI5NzkxNzEsImlhdCI6MTUxMjk3ODg3MSwiY2xpZW50SWQiOiJfIiwicHJvamVjdElkIjoiY2o5dnAwMzloMTl2bjAxNDhlc3UzbnYzMSIsInBlcm1hbmVudEF1dGhUb2tlbklkIjoiY2piMXdrMHR2NGExNDAxNTRxMXBrMnh0diJ9.WcqQchOGD-BwwwM4Nmh0zYoOpPk7YcGk1qzRcutDxmY',\n serviceId: 'cj9vp039h19vn0148esu3nv31' } } }"

How to reproduce the issue:

import ApolloClient from "apollo-client";
import { HttpLink } from "apollo-link-http";
import { ApolloLink, concat } from "apollo-link";
import { InMemoryCache } from "apollo-cache-inmemory";
import { setContext } from "apollo-link-context";

const authMiddleware = setContext(request => {
  new Promise((success, fail) => {
    AsyncStorage.getItem(ProjectSettings.graphcoolKey).then(token => {
      success({
        headers: {
          authorization: 'Bearer ${token}'
        }
      });
    });
  });
});

const httpLink = new HttpLink({
  uri: ProjectSettings.simpleGraphCoolEndPoint
});

const client = new ApolloClient({
  link: concat(authMiddleware , httpLink),
  cache: new InMemoryCache()
});

I tried a lot of different combinaison :

success({ token: 'async found token' })
success({ auth: 'async found token' })
success({ headers:  { auth: 'async found token' }})
...

Even the simpliest way doesn't send anything

const middleware = setContext((request, previousContext) => ({
  authorization: '1234'
}))