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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def r_oauth_login(self):
 """ Route for OAuth2 Login :param next next url :type str :return: Redirects to OAuth Provider Login URL """

        session['next'] = request.args.get('next','')
        callback_url = self.authcallback
        if callback_url is None:
            callback_url = url_for('.r_oauth_authorized', _external=True)
        return self.authobj.authorize(callback=callback_url)