Validate JWT access_token from AAD Azure Fails

I need to validate a azure jwt access_token from the service I'm working on. We are currently making a request to https://graph.microsoft.com/beta/me. If the request succeeded, the token is valid. Unfortunately we will not be able to keep doing that.

I have tried a variety of ideas for this. None of them with success. Even jwt.io does not recognize the signature, even though jwt kid and the kid from one of the available signatures in jwk_uri matches.

Based on this blog post I have created a following solution (also available on github) .

My implementation is very similar to the blog post with a few changes:

#!/usr/bin/env python2

import jwt
import requests
import sys

from cryptography.x509 import load_pem_x509_certificate
from cryptography.hazmat.backends import default_backend


def get_public_key(access_token):
    """ Retrieve public key for access token """
    token_header = jwt.get_unverified_header(access_token)

    res = requests.get('https://login.microsoftonline.com/common/.well-known/openid-configuration')
    jwk_uri = res.json()['jwks_uri']

    res = requests.get(jwk_uri)
    jwk_keys = res.json()

    x5c = None
    # Iterate JWK keys and extract matching x5c chain
    for key in jwk_keys['keys']:
        if key['kid'] == token_header['kid']:
            x5c = key['x5c']
            break
    else:
        raise Exception('Certificate not found in {}'.format(jwk_uri))

    cert = ''.join([
        '-----BEGIN CERTIFICATE-----\n',
        x5c[0],
        '\n-----END CERTIFICATE-----\n',
    ])
    try:
        public_key =  load_pem_x509_certificate(cert.encode(), default_backend()).public_key()
    except Exception as error:
        raise Exception('Failed to load public key:', error)

    return public_key, key['kid']

def main():
    print '\n'
    if len(sys.argv) < 2 or '-h' in sys.argv:
        print 'Run it again passing acces token:\n\tpython jwt_validation.py <access_token>'
        sys.exit(1)

    access_token = sys.argv[1]
    audience = 'https://graph.microsoft.com'

    public_key, kid = get_public_key(access_token)

    try:
        jwt.decode(
            access_token,
            public_key,
            algorithms='RS256',
            audience=audience,
        )
    except Exception as error:
        print 'key {} did not worked, error:'.format(kid), error
        sys.exit(1)

    print('Key worked!')

if __name__ == '__main__':
    main()

This solution returns Invalid Signature for a valid access_token with the following traceback:

Traceback (most recent call last):
File "jwt_validation/jwt_validation.py", line 63, in <module>
    main()
File "jwt_validation/jwt_validation.py", line 57, in main 
    audience=audience,
File "~/.pyenv/versions/jwt-validation-tool/lib/python2.7/site-packages/jwt/api_jwt.py", line 93, in decode
    jwt, key=key, algorithms=algorithms, options=options, **kwargs
File "~/.pyenv/versions/jwt-validation-tool/lib/python2.7/site-packages/jwt/api_jws.py", line 157, in decode
    key, algorithms)
File "~/.pyenv/versions/jwt-validation-tool/lib/python2.7/site-packages/jwt/api_jws.py", line 224, in _verify_signature
    raise InvalidSignatureError('Signature verification failed')
jwt.exceptions.InvalidSignatureError: Signature verification failed

Any ideas of what I could be wrong would be helpful.