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# Copyright 2017-2018 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 urllib
import json
import time
from jose import jwk, jwt
from jose.utils import base64url_decode
region = 'ap-southeast-2'
userpool_id = 'ap-southeast-2_xxxxxxxxx'
app_client_id = '<ENTER APP CLIENT ID HERE>'
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/
response = urllib.urlopen(keys_url)
keys = json.loads(response.read())['keys']
def lambda_handler(event, context):
token = event['token']
# get the kid from the headers prior to verification
headers = jwt.get_unverified_headers(token)
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)
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': ''}
lambda_handler(event, None)
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