If you want you could add a custom plugin that would take the HTTP server within deepstream and enhance it using express for all your non-deepstream routes, if you raise an issue for it I think it's something that can be done in the near future! But generally wouldn't recommend for non-pet projects since they serve two different purposes.
Ideally you would just configure it using a config file for your permissions (https://deepstream.io/tutorials/core/permission/valve-introd...) and use http auth to authenticate your users (https://deepstream.io/tutorials/core/auth/http-webhook/).
You can see this sort of configuration here https://deepstream.io/guides/live-progress-bar/
If you want you could add a custom plugin that would take the HTTP server within deepstream and enhance it using express for all your non-deepstream routes, if you raise an issue for it I think it's something that can be done in the near future! But generally wouldn't recommend for non-pet projects since they serve two different purposes.
Edit: Also thank you!