text: # Copyright 2016 Google Inc.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #      http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License 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.
  
  """OAuth 2.0 client.
  
  This is a client for interacting with an OAuth 2.0 authorization server's
  token endpoint.
  
  For more information about the token endpoint, see
  `Section 3.1 of rfc6749`_
  
  .. _Section 3.1 of rfc6749: https://tools.ietf.org/html/rfc6749#section-3.2
  """
  
  import datetime
  import json
  
  import six
  from six.moves import http_client
  from six.moves import urllib
  
  from google.auth import _helpers
  from google.auth import exceptions
  from google.auth import jwt
  
  _URLENCODED_CONTENT_TYPE = "application/x-www-form-urlencoded"
  _JWT_GRANT_TYPE = "urn:ietf:params:oauth:grant-type:jwt-bearer"
  _REFRESH_GRANT_TYPE = "refresh_token"
  
  
  def _handle_error_response(response_body):
      """"Translates an error response into an exception.
  
      Args:
          response_body (str): The decoded response data.
  
      Raises:
          google.auth.exceptions.RefreshError
      """
      try:
          error_data = json.loads(response_body)
          error_details = "{}: {}".format(
              error_data["error"], error_data.get("error_description")
          )
      # If no details could be extracted, use the response data.
      except (KeyError, ValueError):
          error_details = response_body
  
      raise exceptions.RefreshError(error_details, response_body)
  
  
  def _parse_expiry(response_data):
      """Parses the expiry field from a response into a datetime.
  
      Args:
          response_data (Mapping): The JSON-parsed response data.
  
      Returns:
          Optional[datetime]: The expiration or ``None`` if no expiration was
              specified.
      """
      expires_in = response_data.get("expires_in", None)
  
      if expires_in is not None:
          return _helpers.utcnow() + datetime.timedelta(seconds=expires_in)
      else:
          return None
  
  
  def _token_endpoint_request(request, token_uri, body):
      """Makes a request to the OAuth 2.0 authorization server's token endpoint.
  
      Args:
          request (google.auth.transport.Request): A callable used to make
              HTTP requests.
          token_uri (str): The OAuth 2.0 authorizations server's token endpoint
              URI.
          body (Mapping[str, str]): The parameters to send in the request body.
  
      Returns:
          Mapping[str, str]: The JSON-decoded response data.
  
      Raises:
          google.auth.exceptions.RefreshError: If the token endpoint returned
              an error.
      """
      body = urllib.parse.urlencode(body)
      headers = {"content-type": _URLENCODED_CONTENT_TYPE}
  
      retry = 0
      # retry to fetch token for maximum of two times if any internal failure
      # occurs.
      while True:
          response = request(method="POST", url=token_uri, headers=headers, body=body)
          response_body = response.data.decode("utf-8")
  
          if response.status == http_client.OK:
              break
          else:
              error_desc = json.loads(response_body).get("error_description") or ""
              if error_desc == "internal_failure" and retry < 1:
                  retry += 1
                  continue
              _handle_error_response(response_body)
  
      response_data = json.loads(response_body)
  
      return response_data
  
  
  def jwt_grant(request, token_uri, assertion):
      """Implements the JWT Profile for OAuth 2.0 Authorization Grants.
  
      For more details, see `rfc7523 section 4`_.
  
      Args:
          request (google.auth.transport.Request): A callable used to make
              HTTP requests.
          token_uri (str): The OAuth 2.0 authorizations server's token endpoint
              URI.
          assertion (str): The OAuth 2.0 assertion.
  
      Returns:
          Tuple[str, Optional[datetime], Mapping[str, str]]: The access token,
              expiration, and additional data returned by the token endpoint.
  
      Raises:
          google.auth.exceptions.RefreshError: If the token endpoint returned
              an error.
  
      .. _rfc7523 section 4: https://tools.ietf.org/html/rfc7523#section-4
      """
      body = {"assertion": assertion, "grant_type": _JWT_GRANT_TYPE}
  
      response_data = _token_endpoint_request(request, token_uri, body)
  
      try:
          access_token = response_data["access_token"]
      except KeyError as caught_exc:
          new_exc = exceptions.RefreshError("No access token in response.", response_data)
          six.raise_from(new_exc, caught_exc)
  
      expiry = _parse_expiry(response_data)
  
      return access_token, expiry, response_data
  
  
  def id_token_jwt_grant(request, token_uri, assertion):
      """Implements the JWT Profile for OAuth 2.0 Authorization Grants, but
      requests an OpenID Connect ID Token instead of an access token.
  
      This is a variant on the standard JWT Profile that is currently unique
      to Google. This was added for the benefit of authenticating to services
      that require ID Tokens instead of access tokens or JWT bearer tokens.
  
      Args:
          request (google.auth.transport.Request): A callable used to make
              HTTP requests.
          token_uri (str): The OAuth 2.0 authorization server's token endpoint
              URI.
          assertion (str): JWT token signed by a service account. The token's
              payload must include a ``target_audience`` claim.
  
      Returns:
          Tuple[str, Optional[datetime], Mapping[str, str]]:
              The (encoded) Open ID Connect ID Token, expiration, and additional
              data returned by the endpoint.
  
      Raises:
          google.auth.exceptions.RefreshError: If the token endpoint returned
              an error.
      """
      body = {"assertion": assertion, "grant_type": _JWT_GRANT_TYPE}
  
      response_data = _token_endpoint_request(request, token_uri, body)
  
      try:
          id_token = response_data["id_token"]
      except KeyError as caught_exc:
          new_exc = exceptions.RefreshError("No ID token in response.", response_data)
          six.raise_from(new_exc, caught_exc)
  
      payload = jwt.decode(id_token, verify=False)
      expiry = datetime.datetime.utcfromtimestamp(payload["exp"])
  
      return id_token, expiry, response_data
  
  
  def refresh_grant(
      request, token_uri, refresh_token, client_id, client_secret, scopes=None
  ):
      """Implements the OAuth 2.0 refresh token grant.
  
      For more details, see `rfc678 section 6`_.
  
      Args:
          request (google.auth.transport.Request): A callable used to make
              HTTP requests.
          token_uri (str): The OAuth 2.0 authorizations server's token endpoint
              URI.
          refresh_token (str): The refresh token to use to get a new access
              token.
          client_id (str): The OAuth 2.0 application's client ID.
          client_secret (str): The Oauth 2.0 appliaction's client secret.
          scopes (Optional(Sequence[str])): Scopes to request. If present, all
              scopes must be authorized for the refresh token. Useful if refresh
              token has a wild card scope (e.g.
              'https://www.googleapis.com/auth/any-api').
  
      Returns:
          Tuple[str, Optional[str], Optional[datetime], Mapping[str, str]]: The
              access token, new refresh token, expiration, and additional data
              returned by the token endpoint.
  
      Raises:
          google.auth.exceptions.RefreshError: If the token endpoint returned
              an error.
  
      .. _rfc6748 section 6: https://tools.ietf.org/html/rfc6749#section-6
      """
      body = {
          "grant_type": _REFRESH_GRANT_TYPE,
          "client_id": client_id,
          "client_secret": client_secret,
          "refresh_token": refresh_token,
      }
      if scopes:
          body["scope"] = " ".join(scopes)
  
      response_data = _token_endpoint_request(request, token_uri, body)
  
      try:
          access_token = response_data["access_token"]
      except KeyError as caught_exc:
          new_exc = exceptions.RefreshError("No access token in response.", response_data)
          six.raise_from(new_exc, caught_exc)
  
      refresh_token = response_data.get("refresh_token", refresh_token)
      expiry = _parse_expiry(response_data)
  
      return access_token, refresh_token, expiry, response_data
  