Added OAuth2 authentication to apply_issue

third_party/oauth2client/client.py

+# Copyright (C) 2010 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.
+
+"""An OAuth 2.0 client.
+
+Tools for interacting with OAuth 2.0 protected resources.
+"""
+
+__author__ = 'jcgregorio@google.com (Joe Gregorio)'
+
+import base64
+import clientsecrets
+import copy
+import datetime
+from .. import httplib2
+import logging
+import sys
+import time
+import urllib
+import urlparse
+
+from anyjson import simplejson
+
+HAS_OPENSSL = False
+try:
+  from .crypt import Signer
+  from .crypt import make_signed_jwt
+  from .crypt import verify_signed_jwt_with_certs
+  HAS_OPENSSL = True
+except ImportError:
+  pass
+
+try:
+  from urlparse import parse_qsl
+except ImportError:
+  from cgi import parse_qsl
+
+logger = logging.getLogger(__name__)
+
+# Expiry is stored in RFC3339 UTC format
+EXPIRY_FORMAT = '%Y-%m-%dT%H:%M:%SZ'
+
+# Which certs to use to validate id_tokens received.
+ID_TOKEN_VERIFICATON_CERTS = 'https://www.googleapis.com/oauth2/v1/certs'
+
+
+class Error(Exception):
+  """Base error for this module."""
+  pass
+
+
+class FlowExchangeError(Error):
+  """Error trying to exchange an authorization grant for an access token."""
+  pass
+
+
+class AccessTokenRefreshError(Error):
+  """Error trying to refresh an expired access token."""
+  pass
+
+class UnknownClientSecretsFlowError(Error):
+  """The client secrets file called for an unknown type of OAuth 2.0 flow. """
+  pass
+
+
+class AccessTokenCredentialsError(Error):
+  """Having only the access_token means no refresh is possible."""
+  pass
+
+
+class VerifyJwtTokenError(Error):
+  """Could on retrieve certificates for validation."""
+  pass
+
+
+def _abstract():
+  raise NotImplementedError('You need to override this function')
+
+
+class Credentials(object):
+  """Base class for all Credentials objects.
+
+  Subclasses must define an authorize() method that applies the credentials to
+  an HTTP transport.
+
+  Subclasses must also specify a classmethod named 'from_json' that takes a JSON
+  string as input and returns an instaniated Crentials object.
+  """
+
+  NON_SERIALIZED_MEMBERS = ['store']
+
+  def authorize(self, http):
+    """Take an httplib2.Http instance (or equivalent) and
+    authorizes it for the set of credentials, usually by
+    replacing http.request() with a method that adds in
+    the appropriate headers and then delegates to the original
+    Http.request() method.
+    """
+    _abstract()
+
+  def _to_json(self, strip):
+    """Utility function for creating a JSON representation of an instance of Credentials.
+
+    Args:
+      strip: array, An array of names of members to not include in the JSON.
+
+    Returns:
+       string, a JSON representation of this instance, suitable to pass to
+       from_json().
+    """
+    t = type(self)
+    d = copy.copy(self.__dict__)
+    for member in strip:
+      del d[member]
+    if 'token_expiry' in d and isinstance(d['token_expiry'], datetime.datetime):
+      d['token_expiry'] = d['token_expiry'].strftime(EXPIRY_FORMAT)
+    # Add in information we will need later to reconsistitue this instance.
+    d['_class'] = t.__name__
+    d['_module'] = t.__module__
+    return simplejson.dumps(d)
+
+  def to_json(self):
+    """Creating a JSON representation of an instance of Credentials.
+
+    Returns:
+       string, a JSON representation of this instance, suitable to pass to
+       from_json().
+    """
+    return self._to_json(Credentials.NON_SERIALIZED_MEMBERS)
+
+  @classmethod
+  def new_from_json(cls, s):
+    """Utility class method to instantiate a Credentials subclass from a JSON
+    representation produced by to_json().
+
+    Args:
+      s: string, JSON from to_json().
+
+    Returns:
+      An instance of the subclass of Credentials that was serialized with
+      to_json().
+    """
+    data = simplejson.loads(s)
+    # Find and call the right classmethod from_json() to restore the object.
+    module = data['_module']
+    m = __import__(module, fromlist=module.split('.')[:-1])
+    kls = getattr(m, data['_class'])
+    from_json = getattr(kls, 'from_json')
+    return from_json(s)
+
+
+class Flow(object):
+  """Base class for all Flow objects."""
+  pass
+
+
+class Storage(object):
+  """Base class for all Storage objects.
+
+  Store and retrieve a single credential.  This class supports locking
+  such that multiple processes and threads can operate on a single
+  store.
+  """
+
+  def acquire_lock(self):
+    """Acquires any lock necessary to access this Storage.
+
+    This lock is not reentrant."""
+    pass
+
+  def release_lock(self):
+    """Release the Storage lock.
+
+    Trying to release a lock that isn't held will result in a
+    RuntimeError.
+    """
+    pass
+
+  def locked_get(self):
+    """Retrieve credential.
+
+    The Storage lock must be held when this is called.
+
+    Returns:
+      oauth2client.client.Credentials
+    """
+    _abstract()
+
+  def locked_put(self, credentials):
+    """Write a credential.
+
+    The Storage lock must be held when this is called.
+
+    Args:
+      credentials: Credentials, the credentials to store.
+    """
+    _abstract()
+
+  def get(self):
+    """Retrieve credential.
+
+    The Storage lock must *not* be held when this is called.
+
+    Returns:
+      oauth2client.client.Credentials
+    """
+    self.acquire_lock()
+    try:
+      return self.locked_get()
+    finally:
+      self.release_lock()
+
+  def put(self, credentials):
+    """Write a credential.
+
+    The Storage lock must be held when this is called.
+
+    Args:
+      credentials: Credentials, the credentials to store.
+    """
+    self.acquire_lock()
+    try:
+      self.locked_put(credentials)
+    finally:
+      self.release_lock()
+
+
+class OAuth2Credentials(Credentials):
+  """Credentials object for OAuth 2.0.
+
+  Credentials can be applied to an httplib2.Http object using the authorize()
+  method, which then adds the OAuth 2.0 access token to each request.
+
+  OAuth2Credentials objects may be safely pickled and unpickled.
+  """
+
+  def __init__(self, access_token, client_id, client_secret, refresh_token,
+               token_expiry, token_uri, user_agent, id_token=None):
+    """Create an instance of OAuth2Credentials.
+
+    This constructor is not usually called by the user, instead
+    OAuth2Credentials objects are instantiated by the OAuth2WebServerFlow.
+
+    Args:
+      access_token: string, access token.
+      client_id: string, client identifier.
+      client_secret: string, client secret.
+      refresh_token: string, refresh token.
+      token_expiry: datetime, when the access_token expires.
+      token_uri: string, URI of token endpoint.
+      user_agent: string, The HTTP User-Agent to provide for this application.
+      id_token: object, The identity of the resource owner.
+
+    Notes:
+      store: callable, A callable that when passed a Credential
+        will store the credential back to where it came from.
+        This is needed to store the latest access_token if it
+        has expired and been refreshed.
+    """
+    self.access_token = access_token
+    self.client_id = client_id
+    self.client_secret = client_secret
+    self.refresh_token = refresh_token
+    self.store = None
+    self.token_expiry = token_expiry
+    self.token_uri = token_uri
+    self.user_agent = user_agent
+    self.id_token = id_token
+
+    # True if the credentials have been revoked or expired and can't be
+    # refreshed.
+    self.invalid = False
+
+  def to_json(self):
+    return self._to_json(Credentials.NON_SERIALIZED_MEMBERS)
+
+  @classmethod
+  def from_json(cls, s):
+    """Instantiate a Credentials object from a JSON description of it. The JSON
+    should have been produced by calling .to_json() on the object.
+
+    Args:
+      data: dict, A deserialized JSON object.
+
+    Returns:
+      An instance of a Credentials subclass.
+    """
+    data = simplejson.loads(s)
+    if 'token_expiry' in data and not isinstance(data['token_expiry'],
+        datetime.datetime):
+      try:
+        data['token_expiry'] = datetime.datetime.strptime(
+            data['token_expiry'], EXPIRY_FORMAT)
+      except:
+        data['token_expiry'] = None
+    retval = OAuth2Credentials(
+        data['access_token'],
+        data['client_id'],
+        data['client_secret'],
+        data['refresh_token'],
+        data['token_expiry'],
+        data['token_uri'],
+        data['user_agent'],
+        data.get('id_token', None))
+    retval.invalid = data['invalid']
+    return retval
+
+  @property
+  def access_token_expired(self):
+    """True if the credential is expired or invalid.
+
+    If the token_expiry isn't set, we assume the token doesn't expire.
+    """
+    if self.invalid:
+      return True
+
+    if not self.token_expiry:
+      return False
+
+    now = datetime.datetime.utcnow()
+    if now >= self.token_expiry:
+      logger.info('access_token is expired. Now: %s, token_expiry: %s',
+                  now, self.token_expiry)
+      return True
+    return False
+
+  def set_store(self, store):
+    """Set the Storage for the credential.
+
+    Args:
+      store: Storage, an implementation of Stroage object.
+        This is needed to store the latest access_token if it
+        has expired and been refreshed.  This implementation uses
+        locking to check for updates before updating the
+        access_token.
+    """
+    self.store = store
+
+  def _updateFromCredential(self, other):
+    """Update this Credential from another instance."""
+    self.__dict__.update(other.__getstate__())
+
+  def __getstate__(self):
+    """Trim the state down to something that can be pickled."""
+    d = copy.copy(self.__dict__)
+    del d['store']
+    return d
+
+  def __setstate__(self, state):
+    """Reconstitute the state of the object from being pickled."""
+    self.__dict__.update(state)
+    self.store = None
+
+  def _generate_refresh_request_body(self):
+    """Generate the body that will be used in the refresh request."""
+    body = urllib.urlencode({
+        'grant_type': 'refresh_token',
+        'client_id': self.client_id,
+        'client_secret': self.client_secret,
+        'refresh_token': self.refresh_token,
+        })
+    return body
+
+  def _generate_refresh_request_headers(self):
+    """Generate the headers that will be used in the refresh request."""
+    headers = {
+        'content-type': 'application/x-www-form-urlencoded',
+    }
+
+    if self.user_agent is not None:
+      headers['user-agent'] = self.user_agent
+
+    return headers
+
+  def _refresh(self, http_request):
+    """Refreshes the access_token.
+
+    This method first checks by reading the Storage object if available.
+    If a refresh is still needed, it holds the Storage lock until the
+    refresh is completed.
+    """
+    if not self.store:
+      self._do_refresh_request(http_request)
+    else:
+      self.store.acquire_lock()
+      try:
+        new_cred = self.store.locked_get()
+        if (new_cred and not new_cred.invalid and
+            new_cred.access_token != self.access_token):
+          logger.info('Updated access_token read from Storage')
+          self._updateFromCredential(new_cred)
+        else:
+          self._do_refresh_request(http_request)
+      finally:
+        self.store.release_lock()
+
+  def _do_refresh_request(self, http_request):
+    """Refresh the access_token using the refresh_token.
+
+    Args:
+       http: An instance of httplib2.Http.request
+           or something that acts like it.
+
+    Raises:
+      AccessTokenRefreshError: When the refresh fails.
+    """
+    body = self._generate_refresh_request_body()
+    headers = self._generate_refresh_request_headers()
+
+    logger.info('Refresing access_token')
+    resp, content = http_request(
+        self.token_uri, method='POST', body=body, headers=headers)
+    if resp.status == 200:
+      # TODO(jcgregorio) Raise an error if loads fails?
+      d = simplejson.loads(content)
+      self.access_token = d['access_token']
+      self.refresh_token = d.get('refresh_token', self.refresh_token)
+      if 'expires_in' in d:
+        self.token_expiry = datetime.timedelta(
+            seconds=int(d['expires_in'])) + datetime.datetime.utcnow()
+      else:
+        self.token_expiry = None
+      if self.store:
+        self.store.locked_put(self)
+    else:
+      # An {'error':...} response body means the token is expired or revoked,
+      # so we flag the credentials as such.
+      logger.error('Failed to retrieve access token: %s' % content)
+      error_msg = 'Invalid response %s.' % resp['status']
+      try:
+        d = simplejson.loads(content)
+        if 'error' in d:
+          error_msg = d['error']
+          self.invalid = True
+          if self.store:
+            self.store.locked_put(self)
+      except:
+        pass
+      raise AccessTokenRefreshError(error_msg)
+
+  def authorize(self, http):
+    """Authorize an httplib2.Http instance with these credentials.
+
+    Args:
+       http: An instance of httplib2.Http
+           or something that acts like it.
+
+    Returns:
+       A modified instance of http that was passed in.
+
+    Example:
+
+      h = httplib2.Http()
+      h = credentials.authorize(h)
+
+    You can't create a new OAuth subclass of httplib2.Authenication
+    because it never gets passed the absolute URI, which is needed for
+    signing. So instead we have to overload 'request' with a closure
+    that adds in the Authorization header and then calls the original
+    version of 'request()'.
+    """
+    request_orig = http.request
+
+    # The closure that will replace 'httplib2.Http.request'.
+    def new_request(uri, method='GET', body=None, headers=None,
+                    redirections=httplib2.DEFAULT_MAX_REDIRECTS,
+                    connection_type=None):
+      if not self.access_token:
+        logger.info('Attempting refresh to obtain initial access_token')
+        self._refresh(request_orig)
+
+      # Modify the request headers to add the appropriate
+      # Authorization header.
+      if headers is None:
+        headers = {}
+      headers['authorization'] = 'OAuth ' + self.access_token
+
+      if self.user_agent is not None:
+        if 'user-agent' in headers:
+          headers['user-agent'] = self.user_agent + ' ' + headers['user-agent']
+        else:
+          headers['user-agent'] = self.user_agent
+
+      resp, content = request_orig(uri, method, body, headers,
+                                   redirections, connection_type)
+
+      if resp.status == 401:
+        logger.info('Refreshing due to a 401')
+        self._refresh(request_orig)
+        headers['authorization'] = 'OAuth ' + self.access_token
+        return request_orig(uri, method, body, headers,
+                            redirections, connection_type)
+      else:
+        return (resp, content)
+
+    http.request = new_request
+    return http
+
+
+class AccessTokenCredentials(OAuth2Credentials):
+  """Credentials object for OAuth 2.0.
+
+  Credentials can be applied to an httplib2.Http object using the
+  authorize() method, which then signs each request from that object
+  with the OAuth 2.0 access token.  This set of credentials is for the
+  use case where you have acquired an OAuth 2.0 access_token from
+  another place such as a JavaScript client or another web
+  application, and wish to use it from Python. Because only the
+  access_token is present it can not be refreshed and will in time
+  expire.
+
+  AccessTokenCredentials objects may be safely pickled and unpickled.
+
+  Usage:
+    credentials = AccessTokenCredentials('<an access token>',
+      'my-user-agent/1.0')
+    http = httplib2.Http()
+    http = credentials.authorize(http)
+
+  Exceptions:
+    AccessTokenCredentialsExpired: raised when the access_token expires or is
+      revoked.
+  """
+
+  def __init__(self, access_token, user_agent):
+    """Create an instance of OAuth2Credentials
+
+    This is one of the few types if Credentials that you should contrust,
+    Credentials objects are usually instantiated by a Flow.
+
+    Args:
+      access_token: string, access token.
+      user_agent: string, The HTTP User-Agent to provide for this application.
+
+    Notes:
+      store: callable, a callable that when passed a Credential
+        will store the credential back to where it came from.
+    """
+    super(AccessTokenCredentials, self).__init__(
+        access_token,
+        None,
+        None,
+        None,
+        None,
+        None,
+        user_agent)
+
+
+  @classmethod
+  def from_json(cls, s):
+    data = simplejson.loads(s)
+    retval = AccessTokenCredentials(
+        data['access_token'],
+        data['user_agent'])
+    return retval
+
+  def _refresh(self, http_request):
+    raise AccessTokenCredentialsError(
+        "The access_token is expired or invalid and can't be refreshed.")
+
+
+class AssertionCredentials(OAuth2Credentials):
+  """Abstract Credentials object used for OAuth 2.0 assertion grants.
+
+  This credential does not require a flow to instantiate because it
+  represents a two legged flow, and therefore has all of the required
+  information to generate and refresh its own access tokens.  It must
+  be subclassed to generate the appropriate assertion string.
+
+  AssertionCredentials objects may be safely pickled and unpickled.
+  """
+
+  def __init__(self, assertion_type, user_agent,
+               token_uri='https://accounts.google.com/o/oauth2/token',
+               **unused_kwargs):
+    """Constructor for AssertionFlowCredentials.
+
+    Args:
+      assertion_type: string, assertion type that will be declared to the auth
+          server
+      user_agent: string, The HTTP User-Agent to provide for this application.
+      token_uri: string, URI for token endpoint. For convenience
+        defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+    """
+    super(AssertionCredentials, self).__init__(
+        None,
+        None,
+        None,
+        None,
+        None,
+        token_uri,
+        user_agent)
+    self.assertion_type = assertion_type
+
+  def _generate_refresh_request_body(self):
+    assertion = self._generate_assertion()
+
+    body = urllib.urlencode({
+        'assertion_type': self.assertion_type,
+        'assertion': assertion,
+        'grant_type': 'assertion',
+        })
+
+    return body
+
+  def _generate_assertion(self):
+    """Generate the assertion string that will be used in the access token
+    request.
+    """
+    _abstract()
+
+if HAS_OPENSSL:
+  # PyOpenSSL is not a prerequisite for oauth2client, so if it is missing then
+  # don't create the SignedJwtAssertionCredentials or the verify_id_token()
+  # method.
+
+  class SignedJwtAssertionCredentials(AssertionCredentials):
+    """Credentials object used for OAuth 2.0 Signed JWT assertion grants.
+
+    This credential does not require a flow to instantiate because it
+    represents a two legged flow, and therefore has all of the required
+    information to generate and refresh its own access tokens.
+    """
+
+    MAX_TOKEN_LIFETIME_SECS = 3600 # 1 hour in seconds
+
+    def __init__(self,
+        service_account_name,
+        private_key,
+        scope,
+        private_key_password='notasecret',
+        user_agent=None,
+        token_uri='https://accounts.google.com/o/oauth2/token',
+        **kwargs):
+      """Constructor for SignedJwtAssertionCredentials.
+
+      Args:
+        service_account_name: string, id for account, usually an email address.
+        private_key: string, private key in P12 format.
+        scope: string or list of strings, scope(s) of the credentials being
+          requested.
+        private_key_password: string, password for private_key.
+        user_agent: string, HTTP User-Agent to provide for this application.
+        token_uri: string, URI for token endpoint. For convenience
+          defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+        kwargs: kwargs, Additional parameters to add to the JWT token, for
+          example prn=joe@xample.org."""
+
+      super(SignedJwtAssertionCredentials, self).__init__(
+          'http://oauth.net/grant_type/jwt/1.0/bearer',
+          user_agent,
+          token_uri=token_uri,
+          )
+
+      if type(scope) is list:
+        scope = ' '.join(scope)
+      self.scope = scope
+
+      self.private_key = private_key
+      self.private_key_password = private_key_password
+      self.service_account_name = service_account_name
+      self.kwargs = kwargs
+
+    @classmethod
+    def from_json(cls, s):
+      data = simplejson.loads(s)
+      retval = SignedJwtAssertionCredentials(
+          data['service_account_name'],
+          data['private_key'],
+          data['private_key_password'],
+          data['scope'],
+          data['user_agent'],
+          data['token_uri'],
+          data['kwargs']
+          )
+      retval.invalid = data['invalid']
+      return retval
+
+    def _generate_assertion(self):
+      """Generate the assertion that will be used in the request."""
+      now = long(time.time())
+      payload = {
+          'aud': self.token_uri,
+          'scope': self.scope,
+          'iat': now,
+          'exp': now + SignedJwtAssertionCredentials.MAX_TOKEN_LIFETIME_SECS,
+          'iss': self.service_account_name
+      }
+      payload.update(self.kwargs)
+      logging.debug(str(payload))
+
+      return make_signed_jwt(
+          Signer.from_string(self.private_key, self.private_key_password),
+          payload)
+
+
+  def verify_id_token(id_token, audience, http=None,
+      cert_uri=ID_TOKEN_VERIFICATON_CERTS):
+    """Verifies a signed JWT id_token.
+
+    Args:
+      id_token: string, A Signed JWT.
+      audience: string, The audience 'aud' that the token should be for.
+      http: httplib2.Http, instance to use to make the HTTP request. Callers
+        should supply an instance that has caching enabled.
+      cert_uri: string, URI of the certificates in JSON format to
+        verify the JWT against.
+
+    Returns:
+      The deserialized JSON in the JWT.
+
+    Raises:
+      oauth2client.crypt.AppIdentityError if the JWT fails to verify.
+    """
+    if http is None:
+      http = httplib2.Http()
+
+    resp, content = http.request(cert_uri)
+
+    if resp.status == 200:
+      certs = simplejson.loads(content)
+      return verify_signed_jwt_with_certs(id_token, certs, audience)
+    else:
+      raise VerifyJwtTokenError('Status code: %d' % resp.status)
+
+
+def _urlsafe_b64decode(b64string):
+  # Guard against unicode strings, which base64 can't handle.
+  b64string = b64string.encode('ascii')
+  padded = b64string + '=' * (4 - len(b64string) % 4)
+  return base64.urlsafe_b64decode(padded)
+
+
+def _extract_id_token(id_token):
+  """Extract the JSON payload from a JWT.
+
+  Does the extraction w/o checking the signature.
+
+  Args:
+    id_token: string, OAuth 2.0 id_token.
+
+  Returns:
+    object, The deserialized JSON payload.
+  """
+  segments = id_token.split('.')
+
+  if (len(segments) != 3):
+    raise VerifyJwtTokenError(
+      'Wrong number of segments in token: %s' % id_token)
+
+  return simplejson.loads(_urlsafe_b64decode(segments[1]))
+
+
+class OAuth2WebServerFlow(Flow):
+  """Does the Web Server Flow for OAuth 2.0.
+
+  OAuth2Credentials objects may be safely pickled and unpickled.
+  """
+
+  def __init__(self, client_id, client_secret, scope, user_agent=None,
+               auth_uri='https://accounts.google.com/o/oauth2/auth',
+               token_uri='https://accounts.google.com/o/oauth2/token',
+               **kwargs):
+    """Constructor for OAuth2WebServerFlow.
+
+    Args:
+      client_id: string, client identifier.
+      client_secret: string client secret.
+      scope: string or list of strings, scope(s) of the credentials being
+        requested.
+      user_agent: string, HTTP User-Agent to provide for this application.
+      auth_uri: string, URI for authorization endpoint. For convenience
+        defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+      token_uri: string, URI for token endpoint. For convenience
+        defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+      **kwargs: dict, The keyword arguments are all optional and required
+                        parameters for the OAuth calls.
+    """
+    self.client_id = client_id
+    self.client_secret = client_secret
+    if type(scope) is list:
+      scope = ' '.join(scope)
+    self.scope = scope
+    self.user_agent = user_agent
+    self.auth_uri = auth_uri
+    self.token_uri = token_uri
+    self.params = {
+        'access_type': 'offline',
+        }
+    self.params.update(kwargs)
+    self.redirect_uri = None
+
+  def step1_get_authorize_url(self, redirect_uri='oob'):
+    """Returns a URI to redirect to the provider.
+
+    Args:
+      redirect_uri: string, Either the string 'oob' for a non-web-based
+                    application, or a URI that handles the callback from
+                    the authorization server.
+
+    If redirect_uri is 'oob' then pass in the
+    generated verification code to step2_exchange,
+    otherwise pass in the query parameters received
+    at the callback uri to step2_exchange.
+    """
+
+    self.redirect_uri = redirect_uri
+    query = {
+        'response_type': 'code',
+        'client_id': self.client_id,
+        'redirect_uri': redirect_uri,
+        'scope': self.scope,
+        }
+    query.update(self.params)
+    parts = list(urlparse.urlparse(self.auth_uri))
+    query.update(dict(parse_qsl(parts[4]))) # 4 is the index of the query part
+    parts[4] = urllib.urlencode(query)
+    return urlparse.urlunparse(parts)
+
+  def step2_exchange(self, code, http=None):
+    """Exhanges a code for OAuth2Credentials.
+
+    Args:
+      code: string or dict, either the code as a string, or a dictionary
+        of the query parameters to the redirect_uri, which contains
+        the code.
+      http: httplib2.Http, optional http instance to use to do the fetch
+    """
+
+    if not (isinstance(code, str) or isinstance(code, unicode)):
+      code = code['code']
+
+    body = urllib.urlencode({
+        'grant_type': 'authorization_code',
+        'client_id': self.client_id,
+        'client_secret': self.client_secret,
+        'code': code,
+        'redirect_uri': self.redirect_uri,
+        'scope': self.scope,
+        })
+    headers = {
+        'content-type': 'application/x-www-form-urlencoded',
+    }
+
+    if self.user_agent is not None:
+      headers['user-agent'] = self.user_agent
+
+    if http is None:
+      http = httplib2.Http()
+
+    resp, content = http.request(self.token_uri, method='POST', body=body,
+                                 headers=headers)
+    if resp.status == 200:
+      # TODO(jcgregorio) Raise an error if simplejson.loads fails?
+      d = simplejson.loads(content)
+      access_token = d['access_token']
+      refresh_token = d.get('refresh_token', None)
+      token_expiry = None
+      if 'expires_in' in d:
+        token_expiry = datetime.datetime.utcnow() + datetime.timedelta(
+            seconds=int(d['expires_in']))
+
+      if 'id_token' in d:
+        d['id_token'] = _extract_id_token(d['id_token'])
+
+      logger.info('Successfully retrieved access token: %s' % content)
+      return OAuth2Credentials(access_token, self.client_id,
+                               self.client_secret, refresh_token, token_expiry,
+                               self.token_uri, self.user_agent,
+                               id_token=d.get('id_token', None))
+    else:
+      logger.error('Failed to retrieve access token: %s' % content)
+      error_msg = 'Invalid response %s.' % resp['status']
+      try:
+        d = simplejson.loads(content)
+        if 'error' in d:
+          error_msg = d['error']
+      except:
+        pass
+
+      raise FlowExchangeError(error_msg)
+
+def flow_from_clientsecrets(filename, scope, message=None):
+  """Create a Flow from a clientsecrets file.
+
+  Will create the right kind of Flow based on the contents of the clientsecrets
+  file or will raise InvalidClientSecretsError for unknown types of Flows.
+
+  Args:
+    filename: string, File name of client secrets.
+    scope: string or list of strings, scope(s) to request.
+    message: string, A friendly string to display to the user if the
+      clientsecrets file is missing or invalid. If message is provided then
+      sys.exit will be called in the case of an error. If message in not
+      provided then clientsecrets.InvalidClientSecretsError will be raised.
+
+  Returns:
+    A Flow object.
+
+  Raises:
+    UnknownClientSecretsFlowError if the file describes an unknown kind of Flow.
+    clientsecrets.InvalidClientSecretsError if the clientsecrets file is
+      invalid.
+  """
+  try:
+    client_type, client_info = clientsecrets.loadfile(filename)
+    if client_type in [clientsecrets.TYPE_WEB, clientsecrets.TYPE_INSTALLED]:
+        return OAuth2WebServerFlow(
+            client_info['client_id'],
+            client_info['client_secret'],
+            scope,
+            None, # user_agent
+            client_info['auth_uri'],
+            client_info['token_uri'])
+  except clientsecrets.InvalidClientSecretsError:
+    if message:
+      sys.exit(message)
+    else:
+      raise
+  else:
+    raise UnknownClientSecretsFlowError(
+        'This OAuth 2.0 flow is unsupported: "%s"' * client_type)