Add mTLS to the reverse proxy and to the Immich client app and forbid access without it.

The mTLS certs can be self-generated. There are tutorials for generating your own CA and individual mTLS certs for each device. Then you put the ca.pem file in a place accessable by NPM and add a couple of commands to the “Advanced” tab of the Immich proxy host, and you put the mTLS cert on the phone and load it into the Immich app.

mTLS is a super strong method, not only does it serve as great authentication for that particular device, it also checks the TLS connection for tampering so it can’t be hijacked even if somehow you get rogue certificates loaded on your phone, you can revoke certs if your phone gets lost or stolen etc.