API Gateway custom auth

authorizer.js

const accountId = process.env.ACCOUNT_ID;
const region = process.env.REGION;
const basicAuthUsername = process.env.BASIC_AUTH_USERNAME;
const basicAuthPassword = process.env.BASIC_AUTH_PASSWORD;

const validateAuth = authorizationHeader => {
  if (!authorizationHeader) return false;

  const encodedCreds = authorizationHeader.split(" ")[1];
  const plainCreds = new Buffer(encodedCreds, "base64").toString().split(":");
  const username = plainCreds[0];
  const password = plainCreds[1];

  return (
    username === basicAuthUsername &&
    password === basicAuthPassword
  );
};

exports.handler = async function(event) {
  console.log("authorising request", { event });

  const token = event.headers["Authorization"];
  const id = event.requestContext["apiId"];
  const principalId = `arn:aws:execute-api:${region}:${accountId}:${id}/*/*/*/*`;

  let effect = validateAuth(token) ? "Allow" : "Deny";

  const policyDocument = {
    Version: "2012-10-17",
    Statement: [
      {
        Action: "execute-api:Invoke",
        Effect: effect,
        Resource: principalId
      }
    ]
  };

  return { principalId, context: null, policyDocument };
};