The routers or computers you are using for this have to support forwarding traffic. With Linux this is pretty straight forward for other OSes I’m not sure how easy it is.

You can get around this by having tailscale installed on the default gateway (router) of each network. It might be quite a pain for OP to change routers at each location. On the plus side, OpenWRT has some other cool features like PXE booting.

Here is an article about tailscale on an OpenWRT router.

I wish I had setup an identity management system sooner. Been self-hosting for years and about a year ago took the full plunge into setting up all my services behind Authentik. Its a game changer not having to deal with all the usernames and passwords.

In a similar vein, before Authentik, I used Vaultwarden to manage all my credentials. That was also a huge game changer with my significant other. Being able to have them setup their own account and then share credentials as an organization is super handy.