web_service: Change authentication system to use JWT (#4041)

* Change authentication system to JWT

* Address review comments
* Get rid of global variable, fix some documentations, fix a bug when verificating
* Refactor PostJson to avoid code duplication
* Rename jwt_token, add functionality to request a new JWT when getting a 401
* Take bools by value instead of const reference
* Send request again when JWT is invalid and use forward declarations
* Omit brackets

src/common/announce_multiplayer_room.h

@@ -24,6 +24,7 @@ struct WebResult {
     };
     Code result_code;
     std::string result_string;
+    std::string returned_data;
 };
 } // namespace Common