# Source code for tornado.auth

    #!/usr/bin/env python
    #
    # Copyright 2009 Facebook
    #
    # 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.

    """This module contains implementations of various third-party
    authentication schemes.

    All the classes in this file are class mixins designed to be used with
    the `tornado.web.RequestHandler` class.  They are used in two ways:

    * On a login handler, use methods such as ``authenticate_redirect()``,
      ``authorize_redirect()``, and ``get_authenticated_user()`` to
      establish the user's identity and store authentication tokens to your
      database and/or cookies.
    * In non-login handlers, use methods such as ``facebook_request()``
      or ``twitter_request()`` to use the authentication tokens to make
      requests to the respective services.

    They all take slightly different arguments due to the fact all these
    services implement authentication and authorization slightly differently.
    See the individual service classes below for complete documentation.

    Example usage for Google OAuth:

    .. testcode::

        class GoogleOAuth2LoginHandler(tornado.web.RequestHandler,
                                       tornado.auth.GoogleOAuth2Mixin):
            @tornado.gen.coroutine
            def get(self):
                if self.get_argument('code', False):
                    user = yield self.get_authenticated_user(
                        redirect_uri='http://your.site.com/auth/google',
                        code=self.get_argument('code'))
                    # Save the user with e.g. set_secure_cookie
                else:
                    yield self.authorize_redirect(
                        redirect_uri='http://your.site.com/auth/google',
                        client_id=self.settings['google_oauth']['key'],
                        scope=['profile', 'email'],
                        response_type='code',
                        extra_params={'approval_prompt': 'auto'})

    .. testoutput::
       :hide:

    .. versionchanged:: 4.0
       All of the callback interfaces in this module are now guaranteed
       to run their callback with an argument of ``None`` on error.
       Previously some functions would do this while others would simply
       terminate the request on their own.  This change also ensures that
       errors are more consistently reported through the ``Future`` interfaces.
    """

    from __future__ import absolute_import, division, print_function

    import base64
    import binascii
    import functools
    import hashlib
    import hmac
    import time
    import uuid

    from tornado.concurrent import TracebackFuture, return_future, chain_future
    from tornado import gen
    from tornado import httpclient
    from tornado import escape
    from tornado.httputil import url_concat
    from tornado.log import gen_log
    from tornado.stack_context import ExceptionStackContext
    from tornado.util import unicode_type, ArgReplacer, PY3

    if PY3:
        import urllib.parse as urlparse
        import urllib.parse as urllib_parse
        long = int
    else:
        import urlparse
        import urllib as urllib_parse

    class AuthError(Exception):
        pass

    def _auth_future_to_callback(callback, future):
        try:
            result = future.result()
        except AuthError as e:
            gen_log.warning(str(e))
            result = None
        callback(result)

    def _auth_return_future(f):
        """Similar to tornado.concurrent.return_future, but uses the auth
        module's legacy callback interface.

        Note that when using this decorator the ``callback`` parameter
        inside the function will actually be a future.
        """
        replacer = ArgReplacer(f, 'callback')

        @functools.wraps(f)
        def wrapper(*args, **kwargs):
            future = TracebackFuture()
            callback, args, kwargs = replacer.replace(future, args, kwargs)
            if callback is not None:
                future.add_done_callback(
                    functools.partial(_auth_future_to_callback, callback))

            def handle_exception(typ, value, tb):
                if future.done():
                    return False
                else:
                    future.set_exc_info((typ, value, tb))
                    return True
            with ExceptionStackContext(handle_exception):
                f(*args, **kwargs)
            return future
        return wrapper

    class OpenIdMixin(object):
        """Abstract implementation of OpenID and Attribute Exchange.

        Class attributes:

        * ``_OPENID_ENDPOINT``: the identity provider's URI.
        """
        @return_future
        def authenticate_redirect(self, callback_uri=None,
                                  ax_attrs=["name", "email", "language", "username"],
                                  callback=None):
            """Redirects to the authentication URL for this service.

            After authentication, the service will redirect back to the given
            callback URI with additional parameters including ``openid.mode``.

            We request the given attributes for the authenticated user by
            default (name, email, language, and username). If you don't need
            all those attributes for your app, you can request fewer with
            the ax_attrs keyword argument.

            .. versionchanged:: 3.1
               Returns a `.Future` and takes an optional callback.  These are
               not strictly necessary as this method is synchronous,
               but they are supplied for consistency with
               `OAuthMixin.authorize_redirect`.
            """
            callback_uri = callback_uri or self.request.uri
            args = self._openid_args(callback_uri, ax_attrs=ax_attrs)
            self.redirect(self._OPENID_ENDPOINT + "?" + urllib_parse.urlencode(args))
            callback()

        @_auth_return_future
        def get_authenticated_user(self, callback, http_client=None):
            """Fetches the authenticated user data upon redirect.

            This method should be called by the handler that receives the
            redirect from the `authenticate_redirect()` method (which is
            often the same as the one that calls it; in that case you would
            call `get_authenticated_user` if the ``openid.mode`` parameter
            is present and `authenticate_redirect` if it is not).

            The result of this method will generally be used to set a cookie.
            """
            # Verify the OpenID response via direct request to the OP
            args = dict((k, v[-1]) for k, v in self.request.arguments.items())
            args["openid.mode"] = u"check_authentication"
            url = self._OPENID_ENDPOINT
            if http_client is None:
                http_client = self.get_auth_http_client()
            http_client.fetch(url, functools.partial(
                self._on_authentication_verified, callback),
                method="POST", body=urllib_parse.urlencode(args))

        def _openid_args(self, callback_uri, ax_attrs=[], oauth_scope=None):
            url = urlparse.urljoin(self.request.full_url(), callback_uri)
            args = {
                "openid.ns": "http://specs.openid.net/auth/2.0",
                "openid.claimed_id":
                "http://specs.openid.net/auth/2.0/identifier_select",
                "openid.identity":
                "http://specs.openid.net/auth/2.0/identifier_select",
                "openid.return_to": url,
                "openid.realm": urlparse.urljoin(url, '/'),
                "openid.mode": "checkid_setup",
            }
            if ax_attrs:
                args.update({
                    "openid.ns.ax": "http://openid.net/srv/ax/1.0",
                    "openid.ax.mode": "fetch_request",
                })
                ax_attrs = set(ax_attrs)
                required = []
                if "name" in ax_attrs:
                    ax_attrs -= set(["name", "firstname", "fullname", "lastname"])
                    required += ["firstname", "fullname", "lastname"]
                    args.update({
                        "openid.ax.type.firstname":
                        "http://axschema.org/namePerson/first",
                        "openid.ax.type.fullname":
                        "http://axschema.org/namePerson",
                        "openid.ax.type.lastname":
                        "http://axschema.org/namePerson/last",
                    })
                known_attrs = {
                    "email": "http://axschema.org/contact/email",
                    "language": "http://axschema.org/pref/language",
                    "username": "http://axschema.org/namePerson/friendly",
                }
                for name in ax_attrs:
                    args["openid.ax.type." + name] = known_attrs[name]
                    required.append(name)
                args["openid.ax.required"] = ",".join(required)
            if oauth_scope:
                args.update({
                    "openid.ns.oauth":
                    "http://specs.openid.net/extensions/oauth/1.0",
                    "openid.oauth.consumer": self.request.host.split(":")[0],
                    "openid.oauth.scope": oauth_scope,
                })
            return args

        def _on_authentication_verified(self, future, response):
            if response.error or b"is_valid:true" not in response.body:
                future.set_exception(AuthError(
                    "Invalid OpenID response: %s" % (response.error or
                                                     response.body)))
                return

            # Make sure we got back at least an email from attribute exchange
            ax_ns = None
            for name in self.request.arguments:
                if name.startswith("openid.ns.") and \
                        self.get_argument(name) == u"http://openid.net/srv/ax/1.0":
                    ax_ns = name[10:]
                    break

            def get_ax_arg(uri):
                if not ax_ns:
                    return u""
                prefix = "openid." + ax_ns + ".type."
                ax_name = None
                for name in self.request.arguments.keys():
                    if self.get_argument(name) == uri and name.startswith(prefix):
                        part = name[len(prefix):]
                        ax_name = "openid." + ax_ns + ".value." + part
                        break
                if not ax_name:
                    return u""
                return self.get_argument(ax_name, u"")

            email = get_ax_arg("http://axschema.org/contact/email")
            name = get_ax_arg("http://axschema.org/namePerson")
            first_name = get_ax_arg("http://axschema.org/namePerson/first")
            last_name = get_ax_arg("http://axschema.org/namePerson/last")
            username = get_ax_arg("http://axschema.org/namePerson/friendly")
            locale = get_ax_arg("http://axschema.org/pref/language").lower()
            user = dict()
            name_parts = []
            if first_name:
                user["first_name"] = first_name
                name_parts.append(first_name)
            if last_name:
                user["last_name"] = last_name
                name_parts.append(last_name)
            if name:
                user["name"] = name
            elif name_parts:
                user["name"] = u" ".join(name_parts)
            elif email:
                user["name"] = email.split("@")[0]
            if email:
                user["email"] = email
            if locale:
                user["locale"] = locale
            if username:
                user["username"] = username
            claimed_id = self.get_argument("openid.claimed_id", None)
            if claimed_id:
                user["claimed_id"] = claimed_id
            future.set_result(user)

        def get_auth_http_client(self):
            """Returns the `.AsyncHTTPClient` instance to be used for auth requests.

            May be overridden by subclasses to use an HTTP client other than
            the default.
            """
            return httpclient.AsyncHTTPClient()

    class OAuthMixin(object):
        """Abstract implementation of OAuth 1.0 and 1.0a.

        See `TwitterMixin` below for an example implementation.

        Class attributes:

        * ``_OAUTH_AUTHORIZE_URL``: The service's OAuth authorization url.
        * ``_OAUTH_ACCESS_TOKEN_URL``: The service's OAuth access token url.
        * ``_OAUTH_VERSION``: May be either "1.0" or "1.0a".
        * ``_OAUTH_NO_CALLBACKS``: Set this to True if the service requires
          advance registration of callbacks.

        Subclasses must also override the `_oauth_get_user_future` and
        `_oauth_consumer_token` methods.
        """
        @return_future
        def authorize_redirect(self, callback_uri=None, extra_params=None,
                               http_client=None, callback=None):
            """Redirects the user to obtain OAuth authorization for this service.

            The ``callback_uri`` may be omitted if you have previously
            registered a callback URI with the third-party service.  For
            some services (including Friendfeed), you must use a
            previously-registered callback URI and cannot specify a
            callback via this method.

            This method sets a cookie called ``_oauth_request_token`` which is
            subsequently used (and cleared) in `get_authenticated_user` for
            security purposes.

            Note that this method is asynchronous, although it calls
            `.RequestHandler.finish` for you so it may not be necessary
            to pass a callback or use the `.Future` it returns.  However,
            if this method is called from a function decorated with
            `.gen.coroutine`, you must call it with ``yield`` to keep the
            response from being closed prematurely.

            .. versionchanged:: 3.1
               Now returns a `.Future` and takes an optional callback, for
               compatibility with `.gen.coroutine`.
            """
            if callback_uri and getattr(self, "_OAUTH_NO_CALLBACKS", False):
                raise Exception("This service does not support oauth_callback")
            if http_client is None:
                http_client = self.get_auth_http_client()
            if getattr(self, "_OAUTH_VERSION", "1.0a") == "1.0a":
                http_client.fetch(
                    self._oauth_request_token_url(callback_uri=callback_uri,
                                                  extra_params=extra_params),
                    functools.partial(
                        self._on_request_token,
                        self._OAUTH_AUTHORIZE_URL,
                        callback_uri,
                        callback))
            else:
                http_client.fetch(
                    self._oauth_request_token_url(),
                    functools.partial(
                        self._on_request_token, self._OAUTH_AUTHORIZE_URL,
                        callback_uri,
                        callback))

        @_auth_return_future
        def get_authenticated_user(self, callback, http_client=None):
            """Gets the OAuth authorized user and access token.

            This method should be called from the handler for your
            OAuth callback URL to complete the registration process. We run the
            callback with the authenticated user dictionary.  This dictionary
            will contain an ``access_key`` which can be used to make authorized
            requests to this service on behalf of the user.  The dictionary will
            also contain other fields such as ``name``, depending on the service
            used.
            """
            future = callback
            request_key = escape.utf8(self.get_argument("oauth_token"))
            oauth_verifier = self.get_argument("oauth_verifier", None)
            request_cookie = self.get_cookie("_oauth_request_token")
            if not request_cookie:
                future.set_exception(AuthError(
                    "Missing OAuth request token cookie"))
                return
            self.clear_cookie("_oauth_request_token")
            cookie_key, cookie_secret = [base64.b64decode(escape.utf8(i)) for i in request_cookie.split("|")]
            if cookie_key != request_key:
                future.set_exception(AuthError(
                    "Request token does not match cookie"))
                return
            token = dict(key=cookie_key, secret=cookie_secret)
            if oauth_verifier:
                token["verifier"] = oauth_verifier
            if http_client is None:
                http_client = self.get_auth_http_client()
            http_client.fetch(self._oauth_access_token_url(token),
                              functools.partial(self._on_access_token, callback))

        def _oauth_request_token_url(self, callback_uri=None, extra_params=None):
            consumer_token = self._oauth_consumer_token()
            url = self._OAUTH_REQUEST_TOKEN_URL
            args = dict(
                oauth_consumer_key=escape.to_basestring(consumer_token["key"]),
                oauth_signature_method="HMAC-SHA1",
                oauth_timestamp=str(int(time.time())),
                oauth_nonce=escape.to_basestring(binascii.b2a_hex(uuid.uuid4().bytes)),
                oauth_version="1.0",
            )
            if getattr(self, "_OAUTH_VERSION", "1.0a") == "1.0a":
                if callback_uri == "oob":
                    args["oauth_callback"] = "oob"
                elif callback_uri:
                    args["oauth_callback"] = urlparse.urljoin(
                        self.request.full_url(), callback_uri)
                if extra_params:
                    args.update(extra_params)
                signature = _oauth10a_signature(consumer_token, "GET", url, args)
            else:
                signature = _oauth_signature(consumer_token, "GET", url, args)

            args["oauth_signature"] = signature
            return url + "?" + urllib_parse.urlencode(args)

        def _on_request_token(self, authorize_url, callback_uri, callback,
                              response):
            if response.error:
                raise Exception("Could not get request token: %s" % response.error)
            request_token = _oauth_parse_response(response.body)
            data = (base64.b64encode(escape.utf8(request_token["key"])) + b"|" +
                    base64.b64encode(escape.utf8(request_token["secret"])))
            self.set_cookie("_oauth_request_token", data)
            args = dict(oauth_token=request_token["key"])
            if callback_uri == "oob":
                self.finish(authorize_url + "?" + urllib_parse.urlencode(args))
                callback()
                return
            elif callback_uri:
                args["oauth_callback"] = urlparse.urljoin(
                    self.request.full_url(), callback_uri)
            self.redirect(authorize_url + "?" + urllib_parse.urlencode(args))
            callback()

        def _oauth_access_token_url(self, request_token):
            consumer_token = self._oauth_consumer_token()
            url = self._OAUTH_ACCESS_TOKEN_URL
            args = dict(
                oauth_consumer_key=escape.to_basestring(consumer_token["key"]),
                oauth_token=escape.to_basestring(request_token["key"]),
                oauth_signature_method="HMAC-SHA1",
                oauth_timestamp=str(int(time.time())),
                oauth_nonce=escape.to_basestring(binascii.b2a_hex(uuid.uuid4().bytes)),
                oauth_version="1.0",
            )
            if "verifier" in request_token:
                args["oauth_verifier"] = request_token["verifier"]

            if getattr(self, "_OAUTH_VERSION", "1.0a") == "1.0a":
                signature = _oauth10a_signature(consumer_token, "GET", url, args,
                                                request_token)
            else:
                signature = _oauth_signature(consumer_token, "GET", url, args,
                                             request_token)

            args["oauth_signature"] = signature
            return url + "?" + urllib_parse.urlencode(args)

        def _on_access_token(self, future, response):
            if response.error:
                future.set_exception(AuthError("Could not fetch access token"))
                return

            access_token = _oauth_parse_response(response.body)
            self._oauth_get_user_future(access_token).add_done_callback(
                functools.partial(self._on_oauth_get_user, access_token, future))

        def _oauth_consumer_token(self):
            """Subclasses must override this to return their OAuth consumer keys.

            The return value should be a `dict` with keys ``key`` and ``secret``.
            """
            raise NotImplementedError()

        @return_future
        def _oauth_get_user_future(self, access_token, callback):
            """Subclasses must override this to get basic information about the
            user.

            Should return a `.Future` whose result is a dictionary
            containing information about the user, which may have been
            retrieved by using ``access_token`` to make a request to the
            service.

            The access token will be added to the returned dictionary to make
            the result of `get_authenticated_user`.

            For backwards compatibility, the callback-based ``_oauth_get_user``
            method is also supported.
            """
            # By default, call the old-style _oauth_get_user, but new code
            # should override this method instead.
            self._oauth_get_user(access_token, callback)

        def _oauth_get_user(self, access_token, callback):
            raise NotImplementedError()

        def _on_oauth_get_user(self, access_token, future, user_future):
            if user_future.exception() is not None:
                future.set_exception(user_future.exception())
                return
            user = user_future.result()
            if not user:
                future.set_exception(AuthError("Error getting user"))
                return
            user["access_token"] = access_token
            future.set_result(user)

        def _oauth_request_parameters(self, url, access_token, parameters={},
                                      method="GET"):
            """Returns the OAuth parameters as a dict for the given request.

            parameters should include all POST arguments and query string arguments
            that will be sent with the request.
            """
            consumer_token = self._oauth_consumer_token()
            base_args = dict(
                oauth_consumer_key=escape.to_basestring(consumer_token["key"]),
                oauth_token=escape.to_basestring(access_token["key"]),
                oauth_signature_method="HMAC-SHA1",
                oauth_timestamp=str(int(time.time())),
                oauth_nonce=escape.to_basestring(binascii.b2a_hex(uuid.uuid4().bytes)),
                oauth_version="1.0",
            )
            args = {}
            args.update(base_args)
            args.update(parameters)
            if getattr(self, "_OAUTH_VERSION", "1.0a") == "1.0a":
                signature = _oauth10a_signature(consumer_token, method, url, args,
                                                access_token)
            else:
                signature = _oauth_signature(consumer_token, method, url, args,
                                             access_token)
            base_args["oauth_signature"] = escape.to_basestring(signature)
            return base_args

        def get_auth_http_client(self):
            """Returns the `.AsyncHTTPClient` instance to be used for auth requests.

            May be overridden by subclasses to use an HTTP client other than
            the default.
            """
            return httpclient.AsyncHTTPClient()

    class OAuth2Mixin(object):
        """Abstract implementation of OAuth 2.0.

        See `FacebookGraphMixin` or `GoogleOAuth2Mixin` below for example
        implementations.

        Class attributes:

        * ``_OAUTH_AUTHORIZE_URL``: The service's authorization url.
        * ``_OAUTH_ACCESS_TOKEN_URL``:  The service's access token url.
        """
        @return_future
        def authorize_redirect(self, redirect_uri=None, client_id=None,
                               client_secret=None, extra_params=None,
                               callback=None, scope=None, response_type="code"):
            """Redirects the user to obtain OAuth authorization for this service.

            Some providers require that you register a redirect URL with
            your application instead of passing one via this method. You
            should call this method to log the user in, and then call
            ``get_authenticated_user`` in the handler for your
            redirect URL to complete the authorization process.

            .. versionchanged:: 3.1
               Returns a `.Future` and takes an optional callback.  These are
               not strictly necessary as this method is synchronous,
               but they are supplied for consistency with
               `OAuthMixin.authorize_redirect`.
            """
            args = {
                "redirect_uri": redirect_uri,
                "client_id": client_id,
                "response_type": response_type
            }
            if extra_params:
                args.update(extra_params)
            if scope:
                args['scope'] = ' '.join(scope)
            self.redirect(
                url_concat(self._OAUTH_AUTHORIZE_URL, args))
            callback()

        def _oauth_request_token_url(self, redirect_uri=None, client_id=None,
                                     client_secret=None, code=None,
                                     extra_params=None):
            url = self._OAUTH_ACCESS_TOKEN_URL
            args = dict(
                redirect_uri=redirect_uri,
                code=code,
                client_id=client_id,
                client_secret=client_secret,
            )
            if extra_params:
                args.update(extra_params)
            return url_concat(url, args)

        @_auth_return_future
        def oauth2_request(self, url, callback, access_token=None,
                           post_args=None, **args):
            """Fetches the given URL auth an OAuth2 access token.

            If the request is a POST, ``post_args`` should be provided. Query
            string arguments should be given as keyword arguments.

            Example usage:

            ..testcode::

                class MainHandler(tornado.web.RequestHandler,
                                  tornado.auth.FacebookGraphMixin):
                    @tornado.web.authenticated
                    @tornado.gen.coroutine
                    def get(self):
                        new_entry = yield self.oauth2_request(
                            "https://graph.facebook.com/me/feed",
                            post_args={"message": "I am posting from my Tornado application!"},
                            access_token=self.current_user["access_token"])

                        if not new_entry:
                            # Call failed; perhaps missing permission?
                            yield self.authorize_redirect()
                            return
                        self.finish("Posted a message!")

            .. testoutput::
               :hide:

            .. versionadded:: 4.3
            """
            all_args = {}
            if access_token:
                all_args["access_token"] = access_token
                all_args.update(args)

            if all_args:
                url += "?" + urllib_parse.urlencode(all_args)
            callback = functools.partial(self._on_oauth2_request, callback)
            http = self.get_auth_http_client()
            if post_args is not None:
                http.fetch(url, method="POST", body=urllib_parse.urlencode(post_args),
                           callback=callback)
            else:
                http.fetch(url, callback=callback)

        def _on_oauth2_request(self, future, response):
            if response.error:
                future.set_exception(AuthError("Error response %s fetching %s" %
                                               (response.error, response.request.url)))
                return

            future.set_result(escape.json_decode(response.body))

        def get_auth_http_client(self):
            """Returns the `.AsyncHTTPClient` instance to be used for auth requests.

            May be overridden by subclasses to use an HTTP client other than
            the default.

            .. versionadded:: 4.3
            """
            return httpclient.AsyncHTTPClient()

    class TwitterMixin(OAuthMixin):
        """Twitter OAuth authentication.

        To authenticate with Twitter, register your application with
        Twitter at http://twitter.com/apps. Then copy your Consumer Key
        and Consumer Secret to the application
        `~tornado.web.Application.settings` ``twitter_consumer_key`` and
        ``twitter_consumer_secret``. Use this mixin on the handler for the
        URL you registered as your application's callback URL.

        When your application is set up, you can use this mixin like this
        to authenticate the user with Twitter and get access to their stream:

        .. testcode::

            class TwitterLoginHandler(tornado.web.RequestHandler,
                                      tornado.auth.TwitterMixin):
                @tornado.gen.coroutine
                def get(self):
                    if self.get_argument("oauth_token", None):
                        user = yield self.get_authenticated_user()
                        # Save the user using e.g. set_secure_cookie()
                    else:
                        yield self.authorize_redirect()

        .. testoutput::
           :hide:

        The user object returned by `~OAuthMixin.get_authenticated_user`
        includes the attributes ``username``, ``name``, ``access_token``,
        and all of the custom Twitter user attributes described at
        https://dev.twitter.com/docs/api/1.1/get/users/show
        """
        _OAUTH_REQUEST_TOKEN_URL = "https://api.twitter.com/oauth/request_token"
        _OAUTH_ACCESS_TOKEN_URL = "https://api.twitter.com/oauth/access_token"
        _OAUTH_AUTHORIZE_URL = "https://api.twitter.com/oauth/authorize"
        _OAUTH_AUTHENTICATE_URL = "https://api.twitter.com/oauth/authenticate"
        _OAUTH_NO_CALLBACKS = False
        _TWITTER_BASE_URL = "https://api.twitter.com/1.1"

        @return_future
        def authenticate_redirect(self, callback_uri=None, callback=None):
            """Just like `~OAuthMixin.authorize_redirect`, but
            auto-redirects if authorized.

            This is generally the right interface to use if you are using
            Twitter for single-sign on.

            .. versionchanged:: 3.1
               Now returns a `.Future` and takes an optional callback, for
               compatibility with `.gen.coroutine`.
            """
            http = self.get_auth_http_client()
            http.fetch(self._oauth_request_token_url(callback_uri=callback_uri),
                       functools.partial(
                           self._on_request_token, self._OAUTH_AUTHENTICATE_URL,
                           None, callback))

        @_auth_return_future
        def twitter_request(self, path, callback=None, access_token=None,
                            post_args=None, **args):
            """Fetches the given API path, e.g., ``statuses/user_timeline/btaylor``

            The path should not include the format or API version number.
            (we automatically use JSON format and API version 1).

            If the request is a POST, ``post_args`` should be provided. Query
            string arguments should be given as keyword arguments.

            All the Twitter methods are documented at http://dev.twitter.com/

            Many methods require an OAuth access token which you can
            obtain through `~OAuthMixin.authorize_redirect` and
            `~OAuthMixin.get_authenticated_user`. The user returned through that
            process includes an 'access_token' attribute that can be used
            to make authenticated requests via this method. Example
            usage:

            .. testcode::

                class MainHandler(tornado.web.RequestHandler,
                                  tornado.auth.TwitterMixin):
                    @tornado.web.authenticated
                    @tornado.gen.coroutine
                    def get(self):
                        new_entry = yield self.twitter_request(
                            "/statuses/update",
                            post_args={"status": "Testing Tornado Web Server"},
                            access_token=self.current_user["access_token"])
                        if not new_entry:
                            # Call failed; perhaps missing permission?
                            yield self.authorize_redirect()
                            return
                        self.finish("Posted a message!")

            .. testoutput::
               :hide:

            """
            if path.startswith('http:') or path.startswith('https:'):
                # Raw urls are useful for e.g. search which doesn't follow the
                # usual pattern: http://search.twitter.com/search.json
                url = path
            else:
                url = self._TWITTER_BASE_URL + path + ".json"
            # Add the OAuth resource request signature if we have credentials
            if access_token:
                all_args = {}
                all_args.update(args)
                all_args.update(post_args or {})
                method = "POST" if post_args is not None else "GET"
                oauth = self._oauth_request_parameters(
                    url, access_token, all_args, method=method)
                args.update(oauth)
            if args:
                url += "?" + urllib_parse.urlencode(args)
            http = self.get_auth_http_client()
            http_callback = functools.partial(self._on_twitter_request, callback)
            if post_args is not None:
                http.fetch(url, method="POST", body=urllib_parse.urlencode(post_args),
                           callback=http_callback)
            else:
                http.fetch(url, callback=http_callback)

        def _on_twitter_request(self, future, response):
            if response.error:
                future.set_exception(AuthError(
                    "Error response %s fetching %s" % (response.error,
                                                       response.request.url)))
                return
            future.set_result(escape.json_decode(response.body))

        def _oauth_consumer_token(self):
            self.require_setting("twitter_consumer_key", "Twitter OAuth")
            self.require_setting("twitter_consumer_secret", "Twitter OAuth")
            return dict(
                key=self.settings["twitter_consumer_key"],
                secret=self.settings["twitter_consumer_secret"])

        @gen.coroutine
        def _oauth_get_user_future(self, access_token):
            user = yield self.twitter_request(
                "/account/verify_credentials",
                access_token=access_token)
            if user:
                user["username"] = user["screen_name"]
            raise gen.Return(user)

    class GoogleOAuth2Mixin(OAuth2Mixin):
        """Google authentication using OAuth2.

        In order to use, register your application with Google and copy the
        relevant parameters to your application settings.

        * Go to the Google Dev Console at http://console.developers.google.com
        * Select a project, or create a new one.
        * In the sidebar on the left, select APIs & Auth.
        * In the list of APIs, find the Google+ API service and set it to ON.
        * In the sidebar on the left, select Credentials.
        * In the OAuth section of the page, select Create New Client ID.
        * Set the Redirect URI to point to your auth handler
        * Copy the "Client secret" and "Client ID" to the application settings as
          {"google_oauth": {"key": CLIENT_ID, "secret": CLIENT_SECRET}}

        .. versionadded:: 3.2
        """
        _OAUTH_AUTHORIZE_URL = "https://accounts.google.com/o/oauth2/auth"
        _OAUTH_ACCESS_TOKEN_URL = "https://accounts.google.com/o/oauth2/token"
        _OAUTH_USERINFO_URL = "https://www.googleapis.com/oauth2/v1/userinfo"
        _OAUTH_NO_CALLBACKS = False
        _OAUTH_SETTINGS_KEY = 'google_oauth'

        @_auth_return_future
        def get_authenticated_user(self, redirect_uri, code, callback):
            """Handles the login for the Google user, returning an access token.

            The result is a dictionary containing an ``access_token`` field
            ([among others](https://developers.google.com/identity/protocols/OAuth2WebServer#handlingtheresponse)).
            Unlike other ``get_authenticated_user`` methods in this package,
            this method does not return any additional information about the user.
            The returned access token can be used with `OAuth2Mixin.oauth2_request`
            to request additional information (perhaps from
            ``https://www.googleapis.com/oauth2/v2/userinfo``)

            Example usage:

            .. testcode::

                class GoogleOAuth2LoginHandler(tornado.web.RequestHandler,
                                               tornado.auth.GoogleOAuth2Mixin):
                    @tornado.gen.coroutine
                    def get(self):
                        if self.get_argument('code', False):
                            access = yield self.get_authenticated_user(
                                redirect_uri='http://your.site.com/auth/google',
                                code=self.get_argument('code'))
                            user = yield self.oauth2_request(
                                "https://www.googleapis.com/oauth2/v1/userinfo",
                                access_token=access["access_token"])
                            # Save the user and access token with
                            # e.g. set_secure_cookie.
                        else:
                            yield self.authorize_redirect(
                                redirect_uri='http://your.site.com/auth/google',
                                client_id=self.settings['google_oauth']['key'],
                                scope=['profile', 'email'],
                                response_type='code',
                                extra_params={'approval_prompt': 'auto'})

            .. testoutput::
               :hide:

            """
            http = self.get_auth_http_client()
            body = urllib_parse.urlencode({
                "redirect_uri": redirect_uri,
                "code": code,
                "client_id": self.settings[self._OAUTH_SETTINGS_KEY]['key'],
                "client_secret": self.settings[self._OAUTH_SETTINGS_KEY]['secret'],
                "grant_type": "authorization_code",
            })

            http.fetch(self._OAUTH_ACCESS_TOKEN_URL,
                       functools.partial(self._on_access_token, callback),
                       method="POST", headers={'Content-Type': 'application/x-www-form-urlencoded'}, body=body)

        def _on_access_token(self, future, response):
            """Callback function for the exchange to the access token."""
            if response.error:
                future.set_exception(AuthError('Google auth error: %s' % str(response)))
                return

            args = escape.json_decode(response.body)
            future.set_result(args)

    class FacebookGraphMixin(OAuth2Mixin):
        """Facebook authentication using the new Graph API and OAuth2."""
        _OAUTH_ACCESS_TOKEN_URL = "https://graph.facebook.com/oauth/access_token?"
        _OAUTH_AUTHORIZE_URL = "https://www.facebook.com/dialog/oauth?"
        _OAUTH_NO_CALLBACKS = False
        _FACEBOOK_BASE_URL = "https://graph.facebook.com"

        @_auth_return_future
        def get_authenticated_user(self, redirect_uri, client_id, client_secret,
                                   code, callback, extra_fields=None):
            """Handles the login for the Facebook user, returning a user object.

            Example usage:

            .. testcode::

                class FacebookGraphLoginHandler(tornado.web.RequestHandler,
                                                tornado.auth.FacebookGraphMixin):
                  @tornado.gen.coroutine
                  def get(self):
                      if self.get_argument("code", False):
                          user = yield self.get_authenticated_user(
                              redirect_uri='/auth/facebookgraph/',
                              client_id=self.settings["facebook_api_key"],
                              client_secret=self.settings["facebook_secret"],
                              code=self.get_argument("code"))
                          # Save the user with e.g. set_secure_cookie
                      else:
                          yield self.authorize_redirect(
                              redirect_uri='/auth/facebookgraph/',
                              client_id=self.settings["facebook_api_key"],
                              extra_params={"scope": "read_stream,offline_access"})

            .. testoutput::
               :hide:

            This method returns a dictionary which may contain the following fields:

            * ``access_token``, a string which may be passed to `facebook_request`
            * ``session_expires``, an integer encoded as a string representing
              the time until the access token expires in seconds. This field should
              be used like ``int(user['session_expires'])``; in a future version of
              Tornado it will change from a string to an integer.
            * ``id``, ``name``, ``first_name``, ``last_name``, ``locale``, ``picture``,
              ``link``, plus any fields named in the ``extra_fields`` argument. These
              fields are copied from the Facebook graph API `user object <https://developers.facebook.com/docs/graph-api/reference/user>`_

            .. versionchanged:: 4.5
               The ``session_expires`` field was updated to support changes made to the
               Facebook API in March 2017.
            """
            http = self.get_auth_http_client()
            args = {
                "redirect_uri": redirect_uri,
                "code": code,
                "client_id": client_id,
                "client_secret": client_secret,
            }

            fields = set(['id', 'name', 'first_name', 'last_name',
                          'locale', 'picture', 'link'])
            if extra_fields:
                fields.update(extra_fields)

            http.fetch(self._oauth_request_token_url(**args),
                       functools.partial(self._on_access_token, redirect_uri, client_id,
                                         client_secret, callback, fields))

        def _on_access_token(self, redirect_uri, client_id, client_secret,
                             future, fields, response):
            if response.error:
                future.set_exception(AuthError('Facebook auth error: %s' % str(response)))
                return

            args = escape.json_decode(response.body)
            session = {
                "access_token": args.get("access_token"),
                "expires_in": args.get("expires_in")
            }

            self.facebook_request(
                path="/me",
                callback=functools.partial(
                    self._on_get_user_info, future, session, fields),
                access_token=session["access_token"],
                appsecret_proof=hmac.new(key=client_secret.encode('utf8'),
                                         msg=session["access_token"].encode('utf8'),
                                         digestmod=hashlib.sha256).hexdigest(),
                fields=",".join(fields)
            )

        def _on_get_user_info(self, future, session, fields, user):
            if user is None:
                future.set_result(None)
                return

            fieldmap = {}
            for field in fields:
                fieldmap[field] = user.get(field)

            # session_expires is converted to str for compatibility with
            # older versions in which the server used url-encoding and
            # this code simply returned the string verbatim.
            # This should change in Tornado 5.0.
            fieldmap.update({"access_token": session["access_token"],
                             "session_expires": str(session.get("expires_in"))})
            future.set_result(fieldmap)

        @_auth_return_future
        def facebook_request(self, path, callback, access_token=None,
                             post_args=None, **args):
            """Fetches the given relative API path, e.g., "/btaylor/picture"

            If the request is a POST, ``post_args`` should be provided. Query
            string arguments should be given as keyword arguments.

            An introduction to the Facebook Graph API can be found at
            http://developers.facebook.com/docs/api

            Many methods require an OAuth access token which you can
            obtain through `~OAuth2Mixin.authorize_redirect` and
            `get_authenticated_user`. The user returned through that
            process includes an ``access_token`` attribute that can be
            used to make authenticated requests via this method.

            Example usage:

            ..testcode::

                class MainHandler(tornado.web.RequestHandler,
                                  tornado.auth.FacebookGraphMixin):
                    @tornado.web.authenticated
                    @tornado.gen.coroutine
                    def get(self):
                        new_entry = yield self.facebook_request(
                            "/me/feed",
                            post_args={"message": "I am posting from my Tornado application!"},
                            access_token=self.current_user["access_token"])

                        if not new_entry:
                            # Call failed; perhaps missing permission?
                            yield self.authorize_redirect()
                            return
                        self.finish("Posted a message!")

            .. testoutput::
               :hide:

            The given path is relative to ``self._FACEBOOK_BASE_URL``,
            by default "https://graph.facebook.com".

            This method is a wrapper around `OAuth2Mixin.oauth2_request`;
            the only difference is that this method takes a relative path,
            while ``oauth2_request`` takes a complete url.

            .. versionchanged:: 3.1
               Added the ability to override ``self._FACEBOOK_BASE_URL``.
            """
            url = self._FACEBOOK_BASE_URL + path
            # Thanks to the _auth_return_future decorator, our "callback"
            # argument is a Future, which we cannot pass as a callback to
            # oauth2_request. Instead, have oauth2_request return a
            # future and chain them together.
            oauth_future = self.oauth2_request(url, access_token=access_token,
                                               post_args=post_args, **args)
            chain_future(oauth_future, callback)

    def _oauth_signature(consumer_token, method, url, parameters={}, token=None):
        """Calculates the HMAC-SHA1 OAuth signature for the given request.

        See http://oauth.net/core/1.0/#signing_process
        """
        parts = urlparse.urlparse(url)
        scheme, netloc, path = parts[:3]
        normalized_url = scheme.lower() + "://" + netloc.lower() + path

        base_elems = []
        base_elems.append(method.upper())
        base_elems.append(normalized_url)
        base_elems.append("&".join("%s=%s" % (k, _oauth_escape(str(v)))
                                   for k, v in sorted(parameters.items())))
        base_string = "&".join(_oauth_escape(e) for e in base_elems)

        key_elems = [escape.utf8(consumer_token["secret"])]
        key_elems.append(escape.utf8(token["secret"] if token else ""))
        key = b"&".join(key_elems)

        hash = hmac.new(key, escape.utf8(base_string), hashlib.sha1)
        return binascii.b2a_base64(hash.digest())[:-1]

    def _oauth10a_signature(consumer_token, method, url, parameters={}, token=None):
        """Calculates the HMAC-SHA1 OAuth 1.0a signature for the given request.

        See http://oauth.net/core/1.0a/#signing_process
        """
        parts = urlparse.urlparse(url)
        scheme, netloc, path = parts[:3]
        normalized_url = scheme.lower() + "://" + netloc.lower() + path

        base_elems = []
        base_elems.append(method.upper())
        base_elems.append(normalized_url)
        base_elems.append("&".join("%s=%s" % (k, _oauth_escape(str(v)))
                                   for k, v in sorted(parameters.items())))

        base_string = "&".join(_oauth_escape(e) for e in base_elems)
        key_elems = [escape.utf8(urllib_parse.quote(consumer_token["secret"], safe='~'))]
        key_elems.append(escape.utf8(urllib_parse.quote(token["secret"], safe='~') if token else ""))
        key = b"&".join(key_elems)

        hash = hmac.new(key, escape.utf8(base_string), hashlib.sha1)
        return binascii.b2a_base64(hash.digest())[:-1]

    def _oauth_escape(val):
        if isinstance(val, unicode_type):
            val = val.encode("utf-8")
        return urllib_parse.quote(val, safe="~")

    def _oauth_parse_response(body):
        # I can't find an officially-defined encoding for oauth responses and
        # have never seen anyone use non-ascii.  Leave the response in a byte
        # string for python 2, and use utf8 on python 3.
        body = escape.native_str(body)
        p = urlparse.parse_qs(body, keep_blank_values=False)
        token = dict(key=p["oauth_token"][0], secret=p["oauth_token_secret"][0])

        # Add the extra parameters the Provider included to the token
        special = ("oauth_token", "oauth_token_secret")
        token.update((k, p[k][0]) for k in p if k not in special)
        return token