How to make a request to Amazon Selling Partner API (SP-API) using AWS SDK?

[ugultopu]

I'm trying to automate my calls to the SP-API by using AWS SDK. For example, for the getMarketplaceParticipations operation, I came up with the following functioning code, which signs the request headers using the signature-v4 module of AWS SDK.

However, the code has a bit more plumbing than I would like and I have a feeling that I could have accomplished this simpler (with less code) if I figured out a way to accomplish this using the API Gateway Client.

So my question is, given the following code, is it possible to simplify it using API Gateway Client or any other way?

const { Sha256 } = require('@aws-crypto/sha256-js');
const { SignatureV4 } = require("@aws-sdk/signature-v4");

const signatureV4 = new SignatureV4({
  credentials: {
    "accessKeyId": "<access key ID>",
    "secretAccessKey": "<secret access key>",
  },
  region: 'us-east-1',
  service: 'execute-api',
  sha256: Sha256,
});

async function getAccessToken() {
  return (await (await fetch(
    'https://api.amazon.com/auth/o2/token',
    {
      method: 'POST',
      body: new URLSearchParams({
        grant_type: 'refresh_token',
        client_id: '<client ID>',
        client_secret: '<client secret>',
        refresh_token: '<refresh token>',
      }),
    },
  )).json()).access_token;
}

async function getSignedHeaders(url, method) {
  return (await signatureV4.sign({
    method,
    hostname: url.hostname,
    path: url.pathname,
    protocol: url.protocol,
    headers: {
      'host': url.hostname,
      'x-amz-access-token': await getAccessToken(),
    },
  })).headers;
}

async function main() {
  const url = new URL('https://sellingpartnerapi-na.amazon.com/sellers/v1/marketplaceParticipations');
  const method = 'GET';
  const headers = await getSignedHeaders(url, method);

  try {
    const response = await (
      await fetch(url, { method, headers })
    ).json();

    console.log(response);
  } catch (error) {
    console.log(error);
  }
}

main();