# Source code for flask_dance.consumer.oauth2

    import json
    import logging

    import flask
    from flask import current_app, redirect, request, url_for
    from oauthlib.common import generate_token
    from oauthlib.oauth2 import MissingCodeError
    from werkzeug.utils import cached_property
    from werkzeug.wrappers import Response

    from .base import (
        BaseOAuthConsumerBlueprint,
        oauth_authorized,
        oauth_before_login,
        oauth_error,
    )
    from .requests import OAuth2Session

    log = logging.getLogger(__name__)

    class OAuth2ConsumerBlueprint(BaseOAuthConsumerBlueprint):
        """
        A subclass of :class:`flask.Blueprint` that sets up OAuth 2 authentication.
        """

        def __init__(
            self,
            name,
            import_name,
            client_id=None,
            client_secret=None,
            *,
            client=None,
            auto_refresh_url=None,
            auto_refresh_kwargs=None,
            scope=None,
            state=None,
            static_folder=None,
            static_url_path=None,
            template_folder=None,
            url_prefix=None,
            subdomain=None,
            url_defaults=None,
            root_path=None,
            login_url=None,
            authorized_url=None,
            base_url=None,
            authorization_url=None,
            authorization_url_params=None,
            token_url=None,
            token_url_params=None,
            redirect_url=None,
            redirect_to=None,
            session_class=None,
            storage=None,
            rule_kwargs=None,
            use_pkce=False,
            code_challenge_method="S256",
            **kwargs,
        ):
            """
            Most of the constructor arguments are forwarded either to the
            :class:`flask.Blueprint` constructor or the
            :class:`requests_oauthlib.OAuth2Session` constructor, including
            ``**kwargs`` (which is forwarded to
            :class:`~requests_oauthlib.OAuth2Session`).
            Only the arguments that are relevant to Flask-Dance are documented here.

            Args:
                base_url: The base URL of the OAuth provider.
                    If specified, all URLs passed to this instance will be
                    resolved relative to this URL.
                authorization_url: The URL specified by the OAuth provider for
                    obtaining an
                    `authorization grant <https://datatracker.ietf.org/doc/html/rfc6749#section-1.3>`__.
                    This can be an fully-qualified URL, or a path that is
                    resolved relative to the ``base_url``.
                authorization_url_params (dict): A dict of extra
                    key-value pairs to include in the query string of the
                    ``authorization_url``, beyond those necessary for a standard
                    OAuth 2 authorization grant request.
                token_url: The URL specified by the OAuth provider for
                    obtaining an
                    `access token <https://datatracker.ietf.org/doc/html/rfc6749#section-1.4>`__.
                    This can be an fully-qualified URL, or a path that is
                    resolved relative to the ``base_url``.
                token_url_params (dict): A dict of extra
                    key-value pairs to include in the query string of the
                    ``token_url``, beyond those necessary for a standard
                    OAuth 2 access token request.
                login_url: The URL route for the ``login`` view that kicks off
                    the OAuth dance. This string will be
                    :ref:`formatted <python:formatstrings>`
                    with the instance so that attributes can be interpolated.
                    Defaults to ``/{bp.name}``, so that the URL is based on the name
                    of the blueprint.
                authorized_url: The URL route for the ``authorized`` view that
                    completes the OAuth dance. This string will be
                    :ref:`formatted <python:formatstrings>`
                    with the instance so that attributes can be interpolated.
                    Defaults to ``/{bp.name}/authorized``, so that the URL is
                    based on the name of the blueprint.
                redirect_url: When the OAuth dance is complete,
                    redirect the user to this URL.
                redirect_to: When the OAuth dance is complete,
                    redirect the user to the URL obtained by calling
                    :func:`~flask.url_for` with this argument. If you do not specify
                    either ``redirect_url`` or ``redirect_to``, the user will be
                    redirected to the root path (``/``).
                session_class: The class to use for creating a Requests session
                    between the consumer (your website) and the provider (e.g.
                    Google). Defaults to
                    :class:`~flask_dance.consumer.requests.OAuth2Session`.
                storage: A token storage class, or an instance of a token storage
                    class, to use for this blueprint. Defaults to
                    :class:`~flask_dance.consumer.storage.session.SessionStorage`.
                rule_kwargs (dict, optional): Additional arguments that should be passed when adding
                    the login and authorized routes. Defaults to ``None``.
                use_pkce: If true then the authorization flow will follow the PKCE (Proof Key for Code Exchange).
                    For more details please refer to `RFC7636 <https://www.rfc-editor.org/rfc/rfc7636#section-4.1>`__
                code_challenge_method: Code challenge method to be used in authorization code flow with PKCE
                    instead of client secret. It will be used only if ``use_pkce`` is set to True.
                    Defaults to ``S256``.
            """
            BaseOAuthConsumerBlueprint.__init__(
                self,
                name,
                import_name,
                static_folder=static_folder,
                static_url_path=static_url_path,
                template_folder=template_folder,
                url_prefix=url_prefix,
                subdomain=subdomain,
                url_defaults=url_defaults,
                root_path=root_path,
                login_url=login_url,
                authorized_url=authorized_url,
                storage=storage,
                rule_kwargs=rule_kwargs,
            )

            self.base_url = base_url
            self.session_class = session_class or OAuth2Session

            # passed to OAuth2Session()
            self._client_id = client_id
            self.client = client
            self.auto_refresh_url = auto_refresh_url
            self.auto_refresh_kwargs = auto_refresh_kwargs
            self.scope = scope
            self.state = state
            self.kwargs = kwargs
            self.client_secret = client_secret

            # used by view functions
            self.authorization_url = authorization_url
            self.authorization_url_params = authorization_url_params or {}
            self.token_url = token_url
            self.token_url_params = token_url_params or {}
            self.redirect_url = redirect_url
            self.redirect_to = redirect_to
            self.code_challenge_method = code_challenge_method
            self.use_pkce = use_pkce

            self.teardown_app_request(self.teardown_session)

        @property
        def client_id(self):
            return self.session.client_id

        @client_id.setter
        def client_id(self, value):
            self.session.client_id = value
            # due to a bug in requests-oauthlib, we need to set this manually
            self.session._client.client_id = value

        @cached_property
        def session(self):
            """
            This is a session between the consumer (your website) and the provider
            (e.g. Google). It is *not* a session between a user of your website
            and your website.
            :return:
            """
            ret = self.session_class(
                client_id=self._client_id,
                client=self.client,
                auto_refresh_url=self.auto_refresh_url,
                auto_refresh_kwargs=self.auto_refresh_kwargs,
                scope=self.scope,
                state=self.state,
                blueprint=self,
                base_url=self.base_url,
                **self.kwargs,
            )

            def token_updater(token):
                self.token = token

            ret.token_updater = token_updater
            return self.session_created(ret)

        def session_created(self, session):
            return session

        def teardown_session(self, exception=None):
            try:
                del self.session
            except KeyError:
                pass

        def login(self):
            log.debug("client_id = %s", self.client_id)
            self.session.redirect_uri = url_for(".authorized", _external=True)
            if self.use_pkce:
                code_verifier = generate_token(length=48)
                code_challenge = self.session._client.create_code_challenge(
                    code_verifier=code_verifier,
                    code_challenge_method=self.code_challenge_method,
                )
                self.authorization_url_params.update(
                    {
                        "code_challenge_method": self.code_challenge_method,
                        "code_challenge": code_challenge,
                    }
                )
                code_verifier_key = f"{self.name}_oauth_code_verifier"
                flask.session[code_verifier_key] = code_verifier
                log.debug("code_verifier = %s", code_verifier)

            url, state = self.session.authorization_url(
                self.authorization_url, state=self.state, **self.authorization_url_params
            )
            state_key = f"{self.name}_oauth_state"
            flask.session[state_key] = state
            log.debug("state = %s", state)
            log.debug("redirect URL = %s", url)
            oauth_before_login.send(self, url=url)
            return redirect(url)

        def authorized(self):
            """
            This is the route/function that the user will be redirected to by
            the provider (e.g. Google) after the user has logged into the
            provider's website and authorized your app to access their account.
            """
            if self.redirect_url:
                next_url = self.redirect_url
            elif self.redirect_to:
                next_url = url_for(self.redirect_to)
            else:
                next_url = "/"
            log.debug("next_url = %s", next_url)

            # check for error in request args
            error = request.args.get("error")
            if error:
                error_desc = request.args.get("error_description")
                error_uri = request.args.get("error_uri")
                log.warning(
                    "OAuth 2 authorization error: %s description: %s uri: %s",
                    error,
                    error_desc,
                    error_uri,
                )
                results = oauth_error.send(
                    self, error=error, error_description=error_desc, error_uri=error_uri
                )
                if results:
                    for _, ret in results:
                        if isinstance(ret, (Response, current_app.response_class)):
                            return ret
                return redirect(next_url)

            state_key = f"{self.name}_oauth_state"
            if state_key not in flask.session:
                # can't validate state, so redirect back to login view
                log.info("state not found, redirecting user to login")
                return redirect(url_for(".login"))

            state = flask.session[state_key]
            log.debug("state = %s", state)
            self.session._state = state
            del flask.session[state_key]

            if self.use_pkce:
                code_verifier_key = f"{self.name}_oauth_code_verifier"
                if code_verifier_key not in flask.session:
                    # can't find code_verifier, so redirect back to login view
                    log.info("code_verifier not found, redirecting user to login")
                    return redirect(url_for(".login"))

                code_verifier = flask.session[code_verifier_key]
                log.debug("code_verifier = %s", code_verifier)
                del flask.session[code_verifier_key]
                self.token_url_params["code_verifier"] = code_verifier

            self.session.redirect_uri = url_for(".authorized", _external=True)

            log.debug("client_id = %s", self.client_id)
            log.debug("client_secret = %s", self.client_secret)
            try:
                token = self.session.fetch_token(
                    self.token_url,
                    authorization_response=request.url,
                    client_secret=self.client_secret,
                    **self.token_url_params,
                )
            except MissingCodeError as e:
                e.args = (
                    e.args[0],
                    "The redirect request did not contain the expected parameters. Instead I got: {}".format(
                        json.dumps(request.args)
                    ),
                )
                raise

            results = oauth_authorized.send(self, token=token) or []
            set_token = True
            for func, ret in results:
                if isinstance(ret, (Response, current_app.response_class)):
                    return ret
                if ret == False:
                    set_token = False

            if set_token:
                try:
                    self.token = token
                except ValueError as error:
                    log.warning("OAuth 2 authorization error: %s", str(error))
                    oauth_error.send(self, error=error)
            return redirect(next_url)