Added OAuth2 authentication to apply_issue

third_party/oauth2client/client.py

Index: third_party/oauth2client/client.py
diff --git a/third_party/oauth2client/client.py b/third_party/oauth2client/client.py
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index 0000000000000000000000000000000000000000..6901f3f38151a2b5ee759f52fc05f687d75df69a
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+# 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 . import GOOGLE_AUTH_URI
+from . import GOOGLE_REVOKE_URI
+from . import GOOGLE_TOKEN_URI
+from . import util
+from .anyjson import simplejson
+
+HAS_OPENSSL = False
+HAS_CRYPTO = False
+try:
+  from . import crypt
+  HAS_CRYPTO = True
+  if crypt.OpenSSLVerifier is not None:
+    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'
+
+# Constant to use for the out of band OAuth 2.0 flow.
+OOB_CALLBACK_URN = 'urn:ietf:wg:oauth:2.0:oob'
+
+# Google Data client libraries may need to set this to [401, 403].
+REFRESH_STATUS_CODES = [401]
+
+
+class Error(Exception):
+  """Base error for this module."""
+
+
+class FlowExchangeError(Error):
+  """Error trying to exchange an authorization grant for an access token."""
+
+
+class AccessTokenRefreshError(Error):
+  """Error trying to refresh an expired access token."""
+
+
+class TokenRevokeError(Error):
+  """Error trying to revoke a token."""
+
+
+class UnknownClientSecretsFlowError(Error):
+  """The client secrets file called for an unknown type of OAuth 2.0 flow. """
+
+
+class AccessTokenCredentialsError(Error):
+  """Having only the access_token means no refresh is possible."""
+
+
+class VerifyJwtTokenError(Error):
+  """Could on retrieve certificates for validation."""
+
+
+class NonAsciiHeaderError(Error):
+  """Header names and values must be ASCII strings."""
+
+
+def _abstract():
+  raise NotImplementedError('You need to override this function')
+
+
+class MemoryCache(object):
+  """httplib2 Cache implementation which only caches locally."""
+
+  def __init__(self):
+    self.cache = {}
+
+  def get(self, key):
+    return self.cache.get(key)
+
+  def set(self, key, value):
+    self.cache[key] = value
+
+  def delete(self, key):
+    self.cache.pop(key, None)
+
+
+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 Credentials object.
+  """
+
+  NON_SERIALIZED_MEMBERS = ['store']
+
+  def authorize(self, http):
+    """Take an httplib2.Http instance (or equivalent) and authorizes it.
+
+    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.
+
+    Args:
+      http: httplib2.Http, an http object to be used to make the refresh
+        request.
+    """
+    _abstract()
+
+  def refresh(self, http):
+    """Forces a refresh of the access_token.
+
+    Args:
+      http: httplib2.Http, an http object to be used to make the refresh
+        request.
+    """
+    _abstract()
+
+  def revoke(self, http):
+    """Revokes a refresh_token and makes the credentials void.
+
+    Args:
+      http: httplib2.Http, an http object to be used to make the revoke
+        request.
+    """
+    _abstract()
+
+  def apply(self, headers):
+    """Add the authorization to the headers.
+
+    Args:
+      headers: dict, the headers to add the Authorization header to.
+    """
+    _abstract()
+
+  def _to_json(self, strip):
+    """Utility function that creates JSON repr. of a Credentials object.
+
+    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:
+      if member in d:
+        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']
+    try:
+      m = __import__(module)
+    except ImportError:
+      # In case there's an object from the old package structure, update it
+      module = module.replace('.apiclient', '')
+      m = __import__(module)
+
+    m = __import__(module, fromlist=module.split('.')[:-1])
+    kls = getattr(m, data['_class'])
+    from_json = getattr(kls, 'from_json')
+    return from_json(s)
+
+  @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.
+    """
+    return Credentials()
+
+
+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 locked_delete(self):
+    """Delete a credential.
+
+    The Storage lock must be held when this is called.
+    """
+    _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()
+
+  def delete(self):
+    """Delete credential.
+
+    Frees any resources associated with storing the credential.
+    The Storage lock must *not* be held when this is called.
+
+    Returns:
+      None
+    """
+    self.acquire_lock()
+    try:
+      return self.locked_delete()
+    finally:
+      self.release_lock()
+
+
+def clean_headers(headers):
+  """Forces header keys and values to be strings, i.e not unicode.
+
+  The httplib module just concats the header keys and values in a way that may
+  make the message header a unicode string, which, if it then tries to
+  contatenate to a binary request body may result in a unicode decode error.
+
+  Args:
+    headers: dict, A dictionary of headers.
+
+  Returns:
+    The same dictionary but with all the keys converted to strings.
+  """
+  clean = {}
+  try:
+    for k, v in headers.iteritems():
+      clean[str(k)] = str(v)
+  except UnicodeEncodeError:
+    raise NonAsciiHeaderError(k + ': ' + v)
+  return clean
+
+
+def _update_query_params(uri, params):
+  """Updates a URI with new query parameters.
+
+  Args:
+    uri: string, A valid URI, with potential existing query parameters.
+    params: dict, A dictionary of query parameters.
+
+  Returns:
+    The same URI but with the new query parameters added.
+  """
+  parts = list(urlparse.urlparse(uri))
+  query_params = dict(parse_qsl(parts[4])) # 4 is the index of the query part
+  query_params.update(params)
+  parts[4] = urllib.urlencode(query_params)
+  return urlparse.urlunparse(parts)
+
+
+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.
+  """
+
+  @util.positional(8)
+  def __init__(self, access_token, client_id, client_secret, refresh_token,
+               token_expiry, token_uri, user_agent, revoke_uri=None,
+               id_token=None, token_response=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.
+      revoke_uri: string, URI for revoke endpoint. Defaults to None; a token
+        can't be revoked if this is None.
+      id_token: object, The identity of the resource owner.
+      token_response: dict, the decoded response to the token request. None
+        if a token hasn't been requested yet. Stored because some providers
+        (e.g. wordpress.com) include extra fields that clients may want.
+
+    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.revoke_uri = revoke_uri
+    self.id_token = id_token
+    self.token_response = token_response
+
+    # True if the credentials have been revoked or expired and can't be
+    # refreshed.
+    self.invalid = False
+
+  def authorize(self, http):
+    """Authorize an httplib2.Http instance with these credentials.
+
+    The modified http.request method will add authentication headers to each
+    request and will refresh access_tokens when a 401 is received on a
+    request. In addition the http.request method has a credentials property,
+    http.request.credentials, which is the Credentials object that authorized
+    it.
+
+    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'.
+    @util.positional(1)
+    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 = {}
+      self.apply(headers)
+
+      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, clean_headers(headers),
+                                   redirections, connection_type)
+
+      if resp.status in REFRESH_STATUS_CODES:
+        logger.info('Refreshing due to a %s' % str(resp.status))
+        self._refresh(request_orig)
+        self.apply(headers)
+        return request_orig(uri, method, body, clean_headers(headers),
+                            redirections, connection_type)
+      else:
+        return (resp, content)
+
+    # Replace the request method with our own closure.
+    http.request = new_request
+
+    # Set credentials as a property of the request method.
+    setattr(http.request, 'credentials', self)
+
+    return http
+
+  def refresh(self, http):
+    """Forces a refresh of the access_token.
+
+    Args:
+      http: httplib2.Http, an http object to be used to make the refresh
+        request.
+    """
+    self._refresh(http.request)
+
+  def revoke(self, http):
+    """Revokes a refresh_token and makes the credentials void.
+
+    Args:
+      http: httplib2.Http, an http object to be used to make the revoke
+        request.
+    """
+    self._revoke(http.request)
+
+  def apply(self, headers):
+    """Add the authorization to the headers.
+
+    Args:
+      headers: dict, the headers to add the Authorization header to.
+    """
+    headers['Authorization'] = 'Bearer ' + self.access_token
+
+  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 = cls(
+        data['access_token'],
+        data['client_id'],
+        data['client_secret'],
+        data['refresh_token'],
+        data['token_expiry'],
+        data['token_uri'],
+        data['user_agent'],
+        revoke_uri=data.get('revoke_uri', None),
+        id_token=data.get('id_token', None),
+        token_response=data.get('token_response', 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.
+
+    Args:
+      http_request: callable, a callable that matches the method signature of
+        httplib2.Http.request, used to make the refresh request.
+
+    Raises:
+      AccessTokenRefreshError: When the refresh fails.
+    """
+    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_request: callable, a callable that matches the method signature of
+        httplib2.Http.request, used to make the refresh request.
+
+    Raises:
+      AccessTokenRefreshError: When the refresh fails.
+    """
+    body = self._generate_refresh_request_body()
+    headers = self._generate_refresh_request_headers()
+
+    logger.info('Refreshing 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.token_response = d
+      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.info('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 StandardError:
+        pass
+      raise AccessTokenRefreshError(error_msg)
+
+  def _revoke(self, http_request):
+    """Revokes the refresh_token and deletes the store if available.
+
+    Args:
+      http_request: callable, a callable that matches the method signature of
+        httplib2.Http.request, used to make the revoke request.
+    """
+    self._do_revoke(http_request, self.refresh_token)
+
+  def _do_revoke(self, http_request, token):
+    """Revokes the credentials and deletes the store if available.
+
+    Args:
+      http_request: callable, a callable that matches the method signature of
+        httplib2.Http.request, used to make the refresh request.
+      token: A string used as the token to be revoked. Can be either an
+        access_token or refresh_token.
+
+    Raises:
+      TokenRevokeError: If the revoke request does not return with a 200 OK.
+    """
+    logger.info('Revoking token')
+    query_params = {'token': token}
+    token_revoke_uri = _update_query_params(self.revoke_uri, query_params)
+    resp, content = http_request(token_revoke_uri)
+    if resp.status == 200:
+      self.invalid = True
+    else:
+      error_msg = 'Invalid response %s.' % resp.status
+      try:
+        d = simplejson.loads(content)
+        if 'error' in d:
+          error_msg = d['error']
+      except StandardError:
+        pass
+      raise TokenRevokeError(error_msg)
+
+    if self.store:
+      self.store.delete()
+
+
+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, revoke_uri=None):
+    """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.
+      revoke_uri: string, URI for revoke endpoint. Defaults to None; a token
+        can't be revoked if this is None.
+    """
+    super(AccessTokenCredentials, self).__init__(
+        access_token,
+        None,
+        None,
+        None,
+        None,
+        None,
+        user_agent,
+        revoke_uri=revoke_uri)
+
+
+  @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.')
+
+  def _revoke(self, http_request):
+    """Revokes the access_token and deletes the store if available.
+
+    Args:
+      http_request: callable, a callable that matches the method signature of
+        httplib2.Http.request, used to make the revoke request.
+    """
+    self._do_revoke(http_request, self.access_token)
+
+
+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.
+  """
+
+  @util.positional(2)
+  def __init__(self, assertion_type, user_agent=None,
+               token_uri=GOOGLE_TOKEN_URI,
+               revoke_uri=GOOGLE_REVOKE_URI,
+               **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.
+      revoke_uri: string, URI for revoke endpoint.
+    """
+    super(AssertionCredentials, self).__init__(
+        None,
+        None,
+        None,
+        None,
+        None,
+        token_uri,
+        user_agent,
+        revoke_uri=revoke_uri)
+    self.assertion_type = assertion_type
+
+  def _generate_refresh_request_body(self):
+    assertion = self._generate_assertion()
+
+    body = urllib.urlencode({
+        'assertion': assertion,
+        'grant_type': 'urn:ietf:params:oauth:grant-type:jwt-bearer',
+        })
+
+    return body
+
+  def _generate_assertion(self):
+    """Generate the assertion string that will be used in the access token
+    request.
+    """
+    _abstract()
+
+  def _revoke(self, http_request):
+    """Revokes the access_token and deletes the store if available.
+
+    Args:
+      http_request: callable, a callable that matches the method signature of
+        httplib2.Http.request, used to make the revoke request.
+    """
+    self._do_revoke(http_request, self.access_token)
+
+
+if HAS_CRYPTO:
+  # PyOpenSSL and PyCrypto are not prerequisites 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.
+
+    SignedJwtAssertionCredentials requires either PyOpenSSL, or PyCrypto 2.6 or
+    later. For App Engine you may also consider using AppAssertionCredentials.
+    """
+
+    MAX_TOKEN_LIFETIME_SECS = 3600 # 1 hour in seconds
+
+    @util.positional(4)
+    def __init__(self,
+        service_account_name,
+        private_key,
+        scope,
+        private_key_password='notasecret',
+        user_agent=None,
+        token_uri=GOOGLE_TOKEN_URI,
+        revoke_uri=GOOGLE_REVOKE_URI,
+        **kwargs):
+      """Constructor for SignedJwtAssertionCredentials.
+
+      Args:
+        service_account_name: string, id for account, usually an email address.
+        private_key: string, private key in PKCS12 or PEM format.
+        scope: string or iterable of strings, scope(s) of the credentials being
+          requested.
+        private_key_password: string, password for private_key, unused if
+          private_key is in PEM format.
+        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.
+        revoke_uri: string, URI for revoke endpoint.
+        kwargs: kwargs, Additional parameters to add to the JWT token, for
+          example sub=joe@xample.org."""
+
+      super(SignedJwtAssertionCredentials, self).__init__(
+          None,
+          user_agent=user_agent,
+          token_uri=token_uri,
+          revoke_uri=revoke_uri,
+          )
+
+      self.scope = util.scopes_to_string(scope)
+
+      # Keep base64 encoded so it can be stored in JSON.
+      self.private_key = base64.b64encode(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'],
+          base64.b64decode(data['private_key']),
+          data['scope'],
+          private_key_password=data['private_key_password'],
+          user_agent=data['user_agent'],
+          token_uri=data['token_uri'],
+          **data['kwargs']
+          )
+      retval.invalid = data['invalid']
+      retval.access_token = data['access_token']
+      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)
+      logger.debug(str(payload))
+
+      private_key = base64.b64decode(self.private_key)
+      return crypt.make_signed_jwt(crypt.Signer.from_string(
+          private_key, self.private_key_password), payload)
+
+  # Only used in verify_id_token(), which is always calling to the same URI
+  # for the certs.
+  _cached_http = httplib2.Http(MemoryCache())
+
+  @util.positional(2)
+  def verify_id_token(id_token, audience, http=None,
+      cert_uri=ID_TOKEN_VERIFICATON_CERTS):
+    """Verifies a signed JWT id_token.
+
+    This function requires PyOpenSSL and because of that it does not work on
+    App Engine.
+
+    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 = _cached_http
+
+    resp, content = http.request(cert_uri)
+
+    if resp.status == 200:
+      certs = simplejson.loads(content)
+      return crypt.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]))
+
+
+def _parse_exchange_token_response(content):
+  """Parses response of an exchange token request.
+
+  Most providers return JSON but some (e.g. Facebook) return a
+  url-encoded string.
+
+  Args:
+    content: The body of a response
+
+  Returns:
+    Content as a dictionary object. Note that the dict could be empty,
+    i.e. {}. That basically indicates a failure.
+  """
+  resp = {}
+  try:
+    resp = simplejson.loads(content)
+  except StandardError:
+    # different JSON libs raise different exceptions,
+    # so we just do a catch-all here
+    resp = dict(parse_qsl(content))
+
+  # some providers respond with 'expires', others with 'expires_in'
+  if resp and 'expires' in resp:
+    resp['expires_in'] = resp.pop('expires')
+
+  return resp
+
+
+@util.positional(4)
+def credentials_from_code(client_id, client_secret, scope, code,
+                          redirect_uri='postmessage', http=None,
+                          user_agent=None, token_uri=GOOGLE_TOKEN_URI,
+                          auth_uri=GOOGLE_AUTH_URI,
+                          revoke_uri=GOOGLE_REVOKE_URI):
+  """Exchanges an authorization code for an OAuth2Credentials object.
+
+  Args:
+    client_id: string, client identifier.
+    client_secret: string, client secret.
+    scope: string or iterable of strings, scope(s) to request.
+    code: string, An authroization code, most likely passed down from
+      the client
+    redirect_uri: string, this is generally set to 'postmessage' to match the
+      redirect_uri that the client specified
+    http: httplib2.Http, optional http instance to use to do the fetch
+    token_uri: string, URI for token endpoint. For convenience
+      defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+    auth_uri: string, URI for authorization endpoint. For convenience
+      defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+    revoke_uri: string, URI for revoke endpoint. For convenience
+      defaults to Google's endpoints but any OAuth 2.0 provider can be used.
+
+  Returns:
+    An OAuth2Credentials object.
+
+  Raises:
+    FlowExchangeError if the authorization code cannot be exchanged for an
+     access token
+  """
+  flow = OAuth2WebServerFlow(client_id, client_secret, scope,
+                             redirect_uri=redirect_uri, user_agent=user_agent,
+                             auth_uri=auth_uri, token_uri=token_uri,
+                             revoke_uri=revoke_uri)
+
+  credentials = flow.step2_exchange(code, http=http)
+  return credentials
+
+
+@util.positional(3)
+def credentials_from_clientsecrets_and_code(filename, scope, code,
+                                            message = None,
+                                            redirect_uri='postmessage',
+                                            http=None,
+                                            cache=None):
+  """Returns OAuth2Credentials from a clientsecrets file and an auth code.
+
+  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 clientsecrets.
+    scope: string or iterable of strings, scope(s) to request.
+    code: string, An authorization code, most likely passed down from
+      the client
+    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.
+    redirect_uri: string, this is generally set to 'postmessage' to match the
+      redirect_uri that the client specified
+    http: httplib2.Http, optional http instance to use to do the fetch
+    cache: An optional cache service client that implements get() and set()
+      methods. See clientsecrets.loadfile() for details.
+
+  Returns:
+    An OAuth2Credentials object.
+
+  Raises:
+    FlowExchangeError if the authorization code cannot be exchanged for an
+     access token
+    UnknownClientSecretsFlowError if the file describes an unknown kind of Flow.
+    clientsecrets.InvalidClientSecretsError if the clientsecrets file is
+      invalid.
+  """
+  flow = flow_from_clientsecrets(filename, scope, message=message, cache=cache,
+                                 redirect_uri=redirect_uri)
+  credentials = flow.step2_exchange(code, http=http)
+  return credentials
+
+
+class OAuth2WebServerFlow(Flow):
+  """Does the Web Server Flow for OAuth 2.0.
+
+  OAuth2WebServerFlow objects may be safely pickled and unpickled.
+  """
+
+  @util.positional(4)
+  def __init__(self, client_id, client_secret, scope,
+               redirect_uri=None,
+               user_agent=None,
+               auth_uri=GOOGLE_AUTH_URI,
+               token_uri=GOOGLE_TOKEN_URI,
+               revoke_uri=GOOGLE_REVOKE_URI,
+               **kwargs):
+    """Constructor for OAuth2WebServerFlow.
+
+    The kwargs argument is used to set extra query parameters on the
+    auth_uri. For example, the access_type and approval_prompt
+    query parameters can be set via kwargs.
+
+    Args:
+      client_id: string, client identifier.
+      client_secret: string client secret.
+      scope: string or iterable of strings, scope(s) of the credentials being
+        requested.
+      redirect_uri: string, Either the string 'urn:ietf:wg:oauth:2.0:oob' for
+        a non-web-based application, or a URI that handles the callback from
+        the authorization server.
+      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.
+      revoke_uri: string, URI for revoke 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
+    self.scope = util.scopes_to_string(scope)
+    self.redirect_uri = redirect_uri
+    self.user_agent = user_agent
+    self.auth_uri = auth_uri
+    self.token_uri = token_uri
+    self.revoke_uri = revoke_uri
+    self.params = {
+        'access_type': 'offline',
+        'response_type': 'code',
+    }
+    self.params.update(kwargs)
+
+  @util.positional(1)
+  def step1_get_authorize_url(self, redirect_uri=None):
+    """Returns a URI to redirect to the provider.
+
+    Args:
+      redirect_uri: string, Either the string 'urn:ietf:wg:oauth:2.0:oob' for
+        a non-web-based application, or a URI that handles the callback from
+        the authorization server. This parameter is deprecated, please move to
+        passing the redirect_uri in via the constructor.
+
+    Returns:
+      A URI as a string to redirect the user to begin the authorization flow.
+    """
+    if redirect_uri is not None:
+      logger.warning(('The redirect_uri parameter for'
+          'OAuth2WebServerFlow.step1_get_authorize_url is deprecated. Please'
+          'move to passing the redirect_uri in via the constructor.'))
+      self.redirect_uri = redirect_uri
+
+    if self.redirect_uri is None:
+      raise ValueError('The value of redirect_uri must not be None.')
+
+    query_params = {
+        'client_id': self.client_id,
+        'redirect_uri': self.redirect_uri,
+        'scope': self.scope,
+    }
+    query_params.update(self.params)
+    return _update_query_params(self.auth_uri, query_params)
+
+  @util.positional(2)
+  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
+
+    Returns:
+      An OAuth2Credentials object that can be used to authorize requests.
+
+    Raises:
+      FlowExchangeError if a problem occured exchanging the code for a
+      refresh_token.
+    """
+
+    if not (isinstance(code, str) or isinstance(code, unicode)):
+      if 'code' not in code:
+        if 'error' in code:
+          error_msg = code['error']
+        else:
+          error_msg = 'No code was supplied in the query parameters.'
+        raise FlowExchangeError(error_msg)
+      else:
+        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)
+    d = _parse_exchange_token_response(content)
+    if resp.status == 200 and 'access_token' in d:
+      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')
+      return OAuth2Credentials(access_token, self.client_id,
+                               self.client_secret, refresh_token, token_expiry,
+                               self.token_uri, self.user_agent,
+                               revoke_uri=self.revoke_uri,
+                               id_token=d.get('id_token', None),
+                               token_response=d)
+    else:
+      logger.info('Failed to retrieve access token: %s' % content)
+      if 'error' in d:
+        # you never know what those providers got to say
+        error_msg = unicode(d['error'])
+      else:
+        error_msg = 'Invalid response: %s.' % str(resp.status)
+      raise FlowExchangeError(error_msg)
+
+
+@util.positional(2)
+def flow_from_clientsecrets(filename, scope, redirect_uri=None,
+                            message=None, cache=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 iterable of strings, scope(s) to request.
+    redirect_uri: string, Either the string 'urn:ietf:wg:oauth:2.0:oob' for
+      a non-web-based application, or a URI that handles the callback from
+      the authorization server.
+    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.
+    cache: An optional cache service client that implements get() and set()
+      methods. See clientsecrets.loadfile() for details.
+
+  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, cache=cache)
+    if client_type in (clientsecrets.TYPE_WEB, clientsecrets.TYPE_INSTALLED):
+      constructor_kwargs = {
+          'redirect_uri': redirect_uri,
+          'auth_uri': client_info['auth_uri'],
+          'token_uri': client_info['token_uri'],
+      }
+      revoke_uri = client_info.get('revoke_uri')
+      if revoke_uri is not None:
+        constructor_kwargs['revoke_uri'] = revoke_uri
+      return OAuth2WebServerFlow(
+          client_info['client_id'], client_info['client_secret'],
+          scope, **constructor_kwargs)
+
+  except clientsecrets.InvalidClientSecretsError:
+    if message:
+      sys.exit(message)
+    else:
+      raise
+  else:
+    raise UnknownClientSecretsFlowError(
+        'This OAuth 2.0 flow is unsupported: %r' % client_type)