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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:
 async def oauth2_request( self, url: str, access_token: str = None, post_args: Dict[str, Any] = None, **args: Any ) -> Any: """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 async def get(self):
 new_entry = await 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? await self.authorize_redirect() return self.finish("Posted a message!") .. testoutput:: :hide: .. versionadded:: 4.3 .. versionchanged::: 6.0 The ``callback`` argument was removed. Use the returned awaitable object instead. """

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

        if all_args:
            url += "?" + urllib.parse.urlencode(all_args)
        http = self.get_auth_http_client()
        if post_args is not None:
            response = await http.fetch(
                url, method="POST", body=urllib.parse.urlencode(post_args)
            )
        else:
            response = await http.fetch(url)
        return escape.json_decode(response.body)