Hi,

I've implemented the MongoDbSessionHandler, am also using a Mongo index with expireAfterSeconds to expire the session after a set amount of inactivity.
However even with this set, the gc method still performs a delete operation of it's own.

Have thought about adding an option to the Session Handler to disable that method from doing anything, and also having the write method add the expires index.

Does that sound OK? Happy to code it and send a PR.
Thanks.