Parse GraphQL response to JSON response

I have built a JSON api that receives a json from Postman and transforms it into a graphql request because I need to send a request to an external endpoint that only accepts graphql. So far everything is correct because I get a valid response in graphql. The problem is that I need to transform and parse this graphql response to a JSON response because my api is JSON.

How can I transform and parse my graphql response to JSON to return in my API?

I have used the following link to send graphql requests: https://www.npmjs.com/package/graphql-request

I have the following programming code:

const authenticationGraphQLRequest = async (req: Request, res: Response, _next: NextFunction) => {

  let apiKey: string = req.body.apiKey;
  let password: string = req.body.password;

  if (!apiKey || !password) {
    return res.sendStatus(400);
  }

  let mutationGraphQL: string = generateGraphQLRequest(apiKey, password);

  console.log("REQUEST IN GRAPHQL===>" + mutationGraphQL);

  let responseGraphQL = request(EXTERNAL_ENDPOINT, mutationGraphQL).then((data) => console.log("Response=>" + data))
  console.log("Response in GraphQL===>" + responseGraphQL);

  let responseJSON : string = "";

  return res.status(200).json(responseJSON);
};