AWSCognito-IDTOKEN-DECODER

# Copyright 2017-2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file
# except in compliance with the License. A copy of the License is located at
#
#     http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file is distributed on an "AS IS"
# BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under the License.

import json
import time
import urllib.request
from jose import jwk, jwt
from jose.utils import base64url_decode

region = 'us-west-2'
userpool_id = 'us-west-2_VleK3m9Np'
app_client_id = '4ldj7ouk0hqa0cnijchmu6g8ra'
keys_url = 'https://cognito-idp.{}.amazonaws.com/{}/.well-known/jwks.json'.format(region, userpool_id)
# instead of re-downloading the public keys every time
# we download them only on cold start
# https://aws.amazon.com/blogs/compute/container-reuse-in-lambda/
with urllib.request.urlopen(keys_url) as f:
    response = f.read()
keys = json.loads(response.decode('utf-8'))['keys']

def lambda_handler(event, context):
    token = event['token']
    # get the kid from the headers prior to verification
    headers = jwt.get_unverified_headers(token)
    print("************888888")
    kid = headers['kid']
    # search for the kid in the downloaded public keys
    key_index = -1
    for i in range(len(keys)):
        if kid == keys[i]['kid']:
            key_index = i
            break
    if key_index == -1:
        print('Public key not found in jwks.json')
        return False
    # construct the public key
    public_key = jwk.construct(keys[key_index])
    # get the last two sections of the token,
    # message and signature (encoded in base64)
    message, encoded_signature = str(token).rsplit('.', 1)
    # decode the signature
    decoded_signature = base64url_decode(encoded_signature.encode('utf-8'))
    # verify the signature
    if not public_key.verify(message.encode("utf8"), decoded_signature):
        print('Signature verification failed')
        return False
    print('Signature successfully verified')
    # since we passed the verification, we can now safely
    # use the unverified claims
    claims = jwt.get_unverified_claims(token)
    # additionally we can verify the token expiration
    if time.time() > claims['exp']:
        print('Token is expired')
        return False
    # and the Audience  (use claims['client_id'] if verifying an access token)
    if claims['aud'] != app_client_id:
        print('Token was not issued for this audience')
        return False
    # now we can use the claims
    print(claims)
    roles = []
    if 'cognito:groups' in claims:
        roles.append(claims['cognito:groups'])
    print(roles)
    return claims
        
# the following is useful to make this script executable in both
# AWS Lambda and any other local environments
if __name__ == '__main__':
    # for testing locally you can enter the JWT ID Token here
    event = {'token': 'eyJraWQiOiIrNGVVejhBU0RzOStVNDNjWTZ1TGtHR3k5Q0N1bXp4bzgyWVFVWVdVdVUwPSIsImFsZyI6IlJTMjU2In0.eyJhdF9oYXNoIjoiM0J6WWhOTUtLakpGdVRhM012a3hRUSIsInN1YiI6IjA2MmIwNGIyLWZlMTItNDlkYi1hYThlLTZiMmI0NzcwOTk2MiIsImF1ZCI6IjRsZGo3b3VrMGhxYTBjbmlqY2htdTZnOHJhIiwiZW1haWxfdmVyaWZpZWQiOnRydWUsInRva2VuX3VzZSI6ImlkIiwiYXV0aF90aW1lIjoxNjE0ODU5NTkzLCJpc3MiOiJodHRwczpcL1wvY29nbml0by1pZHAudXMtd2VzdC0yLmFtYXpvbmF3cy5jb21cL3VzLXdlc3QtMl9WbGVLM205TnAiLCJjb2duaXRvOnVzZXJuYW1lIjoiMDYyYjA0YjItZmUxMi00OWRiLWFhOGUtNmIyYjQ3NzA5OTYyIiwiZXhwIjoxNjE0ODYzMTkzLCJpYXQiOjE2MTQ4NTk1OTMsImVtYWlsIjoiZXR3ZWFrMUBnbWFpbC5jb20ifQ.mxlKKe_XIfP4u2X_GdkNUTfOYbCO40GNqNLzHZFPj-AtDIAdlj3LdilHnrR6RsDF6SoJKn-rVydKNjZPJ_hgNwd4n_WTqKMBp8faY90wMwBIdUq-enp8WF5E-taokBCInBDBlRSX7n8rCNNH_avJ6QqqitL8lwbfR33F-39ECdfDGnjK-btkycv8WGrEMTEh5ZWY6xktLcxj-7FGZmgSkeYUrGauvr0wYuvW_q-60TdQRaAxZa13_EurM7HspblnUR-wNbUgd3wkVMedMXCZt4u0qyY5AIIHRmLfKznsTCs-yKwTj883p5IKyPcA4f8hHRy92LqThluuGQZZv7Tc8Q'}
    lambda_handler(event, None)

{"keys":[{"alg":"RS256","e":"AQAB","kid":"+4eUz8ASDs9+U43cY6uLkGGy9CCumzxo82YQUYWUuU0=","kty":"RSA","n":"tIDAQeaRrLDOWS4XUfGlkU5Yykv0RLLW5KqkmB2DUFANYGGsAOU1gqfo6OUjqswCojZbeDRX8l6CIJMdMCEGgHiDFfWF0MMeSXvUuMIK1HT3FQ_iicTAs74t309qGwnhnTWM_alyX_zjHSl-6RqGc-bJT7_8VM95ECXVtYYQpEnVMH9AriClNo1bu2CFzJ2ToRc2CSLRwQiM8zAmfoS0oS68yI7eI4E4mpk1RmaYVRV6cnvjtqUBUwJQeHLt-WxG6gzmrM93K4Jw1t8l_qme73IYIsslUtZ3W9UmpMfJuLrFK2q-fhuLOI2Et4U5oEyZsh_-T5aCZk3SO1NvT930bQ","use":"sig"},{"alg":"RS256","e":"AQAB","kid":"2f9rg3Qdcqiu1jXBUxxtqIrivWJhk9h5I+RhOxDdNDQ=","kty":"RSA","n":"xV9E6dQoqD1kJqK_ZugekMVp_5GeIxpe82tcXh8IKI6JZbvzq3VIrveKcVhu0SVEdrs7-CS2ZWSHbkQvWRa9yWBG54WytyafPC-3F659L4y7SUyBxgx8I6YLeaDgzzp2PnjFIccljNaI-r3X2UK7PcJt-QojPkz6XRYD-NwDDYt6qHbRoUmEHwb2unkLvExTyewxSV4WQiRc8uevEQjc18u5nl0W9dZP7RMeMUORMJ1aKArRWixYRtqIscQJeT6Naf72v_-w1OPkAFR5ryK0zKefuiWS4xtG6d9E8mRBPhy8YIhMiCLqb2JrTEqLPBkaSLvPhZT2MCs0YkNtR9OSOw","use":"sig"}]}