def _PopulateX509(self):
    with self._x509_init_lock:
      if self._x509 is None:

        url = ('https://www.googleapis.com/service_accounts/v1/metadata/x509/%s'
               % urllib.unquote_plus(self._credentials.service_account_email))
        response = urlfetch.fetch(
            url=url,
            validate_certificate=True,
            method=urlfetch.GET)
        if response.status_code != 200:
          raise apiproxy_errors.ApplicationError(
              app_identity_service_pb.AppIdentityServiceError.UNKNOWN_ERROR,
              'Unable to load X509 cert: %s Response code: %i, Content: %s' % (
                  url, response.status_code, response.content))

        message = 'dummy'
        _, signature = self._credentials.sign_blob(message)

        for signing_key, x509 in json.loads(response.content).items():
          der = rsa.pem.load_pem(x509, 'CERTIFICATE')
          asn1_cert, _ = decoder.decode(der, asn1Spec=Certificate())

          key_bitstring = (
              asn1_cert['tbsCertificate']
              ['subjectPublicKeyInfo']
              ['subjectPublicKey'])
          key_bytearray = BitStringToByteString(key_bitstring)

          public_key = rsa.PublicKey.load_pkcs1(key_bytearray, 'DER')
          try:
            if rsa.pkcs1.verify(message, signature, public_key):
              self._x509 = x509
              self._signing_key = signing_key
              return
          except rsa.pkcs1.VerificationError:
            pass

        raise apiproxy_errors.ApplicationError(
            app_identity_service_pb.AppIdentityServiceError.UNKNOWN_ERROR,
            'Unable to find matching X509 cert for private key: %s' % url)
dataset/ETHPy150Open GoogleCloudPlatform/python-compat-runtime/appengine-compat/exported_appengine_sdk/google/appengine/api/app_identity/app_identity_defaultcredentialsbased_stub.py/DefaultCredentialsBasedAppIdentityServiceStub._PopulateX509/original