authorizer lambda

const { CognitoUserPool, CognitoUser, AuthenticationDetails } = require("amazon-cognito-identity-js");

const debug = require("debug");

const error = debug("authorizer:error:lambda");
const verbose = debug("authorizer:verbose:lambda");
// DEBUG : authorizer:*

const cognitoUserPool = () => (
  new CognitoUserPool({
    UserPoolId: config.cognito.USER_POOL_ID,
    ClientId: config.cognito.CLIENT_ID
  })
);


function authenticateUser(auth) {
  const tmp = auth.split(' ');
  const buf = new Buffer(tmp[1], 'base64');
  // create a buffer and tell it the data coming in is base64
  const plain_auth = buf.toString();
  // read it back out as a string

  console.log("Decoded Authorization ", plain_auth);
  const credentials = plain_auth.split(':');
  // split on a ':'

  const poolData = {
    UserPoolId: process.env.USER_POOL_ID,
    // Your user pool id here    
    ClientId: process.env.CLIENT_ID
    // Your client id here
  };
  verbose(poolData);

  const username = credentials[0];
  const password = credentials[1];

  verbose(authenticationDetails);
  const userPool = cognitoUserPool();

  const user = new CognitoUser({ Username: username, Pool: userPool });

  const authenticationData = { Username: username, Password: password };
  const authenticationDetails = new AuthenticationDetails(authenticationData);

  return new Promise((resolve, reject) =>
    user.authenticateUser(authenticationDetails, {
      onSuccess: result => resolve(result),
      onFailure: err => reject(err)
    })
  );
}

exports.handler = async function (event, context, callback) {
  try {
    verbose(event.authorizationToken);
    await authenticateUser(event.authorizationToken);
    callback(null, generatePolicy('user', 'Allow', event.methodArn));
  } catch (err) {
    error(err);
    callback(null, generatePolicy('user', 'Deny', event.methodArn));
  }
};

// Help function to generate an IAM policy
const generatePolicy = function (principalId, effect, resource) {
  const authResponse = {};

  authResponse.principalId = principalId;
  if (effect && resource) {
    const policyDocument = {};
    policyDocument.Version = '2012-10-17';
    policyDocument.Statement = [{
      "Action": 'execute-api:Invoke',
      "Effect": effect,
      "Resource": resource
    }];
    authResponse.policyDocument = policyDocument;
  }
  return authResponse;
}