Access Cognito values in Lambda function

JWT token that is part of the Authorization header is accessible inside the Lambda functions as well. In the below example, I am decoding the JWT token value and checking the values inside it.

This is only possible as we are using the id_token along with access_token value. ID Tokens follow the JWT structure so it is possible to decode and check the values. Access Tokens are not bound to follow the JWT structure and assume to be opaque.

const res = require('./common/res');
const jwtDecode = require('jwt-decode');

const getToken = (header) => {
    return jwtDecode(new Buffer(header.split(" ")[0]).toString());
}

module.exports.handler = async event => {
    console.log(`Cognito User`, event);
    console.log(getToken(event.headers.Authorization));

    return res({body: {
        message: 'This is a test profile message',
        source: event.cognitoPoolClaims // Cognito Pool Claims
    }})
}

/** 
JWT Payload Data

{
  sub: 'b9f37dec-b5bf-4eb1-989f-ae7026715c3d',
  'cognito:groups': [ 'admins' ],
  email_verified: true,
  'cognito:preferred_role': 'arn:aws:iam::XXXXXXXXXX:role/admin-users-serverless-docs',
  iss: 'https://cognito-idp.ap-southeast-1.amazonaws.com/ap-southeast-1_lBwBP9VEb',
  'cognito:username': 'dhaval_admin',
  'cognito:roles': [ 'arn:aws:iam::XXXXXXXXXX:role/admin-users-serverless-docs' ],
  aud: '7fdcfo50mhcqm5ui0pl0lrc88f',
  event_id: '8f233e4a-cd77-4792-89cd-4a29148ecdc2',
  token_use: 'id',
  auth_time: 1595657572,
  exp: 1595661172,
  iat: 1595657572,
  email: '[e-mail]'
}
**/