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

[Vadim Sh., 2014/03/13 18:28:42]

Did you modify this code? I remember it used to be 'import httplib2' (I had to
hack sys.path to make it work). You need to document your modifications
somewhere (like provide revision number of original code plus *.diff you made).
I think we use README.chromium files for this?..

[pgervais, 2014/03/13 22:38:38]

I haven't modified anything in httplib2, I just don't want the users (and the
bots) to be required to install it. Feel free to disagree.

[Vadim Sh., 2014/03/13 22:46:26]

Modifying is fine. What I say is that it's useful to have a diff of that
modification, so that it can be applied when third party code is updated.

Here's how I pulled httplib2 in swarming:
https://code.google.com/p/swarming/source/browse/?repo=client#git%2Fthird_par...

I propose you do something similar here (i.e. specify original revision and
modifications you made in README.chromium).

[pgervais, 2014/03/13 23:04:25]

What you've done looks great. I'll do the same.

+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)