feature: Caddy serves the status page and the Router Manager over HTTPS with a certificate from Let's Encrypt.

README.md

@@ -128,6 +128,10 @@ must have the type shown below; an unknown section or setting is an error.
 | `web` | `port` | integer | `7081` | TCP port of the status web service |
 | `web` | `database` | string | | A PostgreSQL connection string for the refresh tokens; without it, the `vpn-router` database on this host that the web service creates |
 | `web` | `trusted_proxies` | list | the address the call came in on | Addresses whose `X-Forwarded-For` header names the client for the `/auth` rate limit |
+| `https` | `enabled` | boolean | `true` | Caddy serves the status web service and the Router Manager over HTTPS for `wan.local_fqdn` |
+| `https` | `email` | string | | The e-mail address of the Let's Encrypt account |
+| `https` | `web_port` | integer | `7444` | HTTPS port of the status web service |
+| `https` | `manager_port` | integer | `7443` | HTTPS port of the Router Manager |
 
 A minimal site-to-site configuration in `auto` mode:
 
@@ -494,8 +498,8 @@ modules shipped with the package; the configuration file accepts any module inst
 ## Status web service
 
 The `vpn-router-web` service shows the state of the router on the addresses of the interfaces
-`web.listen` names, the internal, the external or both (the default), and `web.port` (7081 by
-default). Its pages `/` and `/status` need no authentication and show no
+`web.listen` names, the internal, the external or both (the default), and on `127.0.0.1`, where
+Caddy calls it (see HTTPS), with `web.port` (7081 by default). Its pages `/` and `/status` need no authentication and show no
 configuration: no key, identity, address or subnet.
 
 The service first makes its signing key and the refresh tokens' database, retrying every 15
@@ -691,20 +695,47 @@ and the facts for `/config` from `/run/vpn-router/web.json` (readable by root on
 `vpn-router-setup` writes; before that file exists the page shows no features.
 `vpn-router-setup` opens `web.port` on the internal and the external interface in the firewall.
 
+## HTTPS
+
+Caddy, from Ubuntu's `caddy` package, serves the status web service on `https.web_port` (7444 by
+default) and, while the Router Manager is installed, the manager on `https.manager_port` (7443),
+both for `wan.local_fqdn`, while `https.enabled` is `true` and `wan.local_fqdn` is set. It obtains
+and renews the certificate from Let's Encrypt with the HTTP challenge, so `wan.local_fqdn` must
+resolve to the router's public address and port 80 must be reachable from the internet; the
+certificate and the ACME account are kept in `/var/lib/caddy`. Port 80 answers the challenge only;
+it does not redirect to HTTPS.
+
+`vpn-router-setup` writes Caddy's configuration to `/etc/caddy/vpn-router.Caddyfile` (root, group
+`caddy`, the group Caddy runs as, mode 0640), which the
+package's drop-in `/usr/lib/systemd/system/caddy.service.d/vpn-router.conf` makes `caddy.service`
+read; `caddy.service` does not start before the file exists, and `/etc/caddy/Caddyfile` is not
+used. Setup starts Caddy, reloads it when the file changes, and stops it and removes the file when
+HTTPS is off. In the firewall it opens port 80 on the external interface and the HTTPS ports on the
+internal and the external interface. Caddy calls both services on `127.0.0.1`, where they listen
+whatever `web.listen` and the manager's `listen` say, and passes the client's address in
+`X-Forwarded-For`, which the manager trusts from `127.0.0.1` and the web service by default, as
+the address the call came in on; a `web.trusted_proxies` that is set must list `127.0.0.1`. The plain HTTP ports stay as
+`web.listen` and the manager's `listen` set them. `docker.exposed_ports` may not take port 80 or
+the HTTPS ports while `https.enabled` is `true`.
+
+```bash
+curl https://router.example.com:7444/status
+```
+
 ## Router Manager
 
 The `vpn-router-manager` package, built in the repository `linux-cloud-router-manager`, is a web
 application that shows the state of the router and manages its users through the status web
 service. It can be installed on the router or on another Linux system. While it is installed on
 the router, `vpn-router-setup` opens its port (`port` in `/etc/vpn-router-manager/manager.json`,
-7080 by default, HTTP; 7443 is kept for it with TLS) on the internal and the external
+7080 by default, HTTP; HTTPS is Caddy's, on `https.manager_port`) on the internal and the external
 interface; restart `vpn-router-setup` after changing it. The manager's `listen` chooses the
 interfaces it listens on.
 
 ## Removal
 
 `apt-get remove` stops `vpn-router-docker`, which removes the Docker rules. It terminates the
-tunnels and takes `wg-quick@wg0` and `openvpn-server@vpn-router` down, but leaves the
+tunnels and takes `wg-quick@wg0`, `openvpn-server@vpn-router` and `caddy` down, but leaves the
 configuration in place. `strongswan` is left enabled, since it is a shared service that
 may be in use by something else.
 
@@ -712,7 +743,8 @@ may be in use by something else.
 `/etc/ufw/before.rules` to its original content, and hands `vpn-router.json` back to `ucf`
 before deleting it so a later reinstall starts clean. It also removes the web service's
 signing key, and the refresh tokens' database, its role and their password file when the package
-created them. Key material and users are never deleted: `/etc/vpn-router/pki`, `/etc/vpn-router/ldap`, the user directory in slapd, the
+created them, and Caddy's configuration `/etc/caddy/vpn-router.Caddyfile`; the certificate in
+`/var/lib/caddy` belongs to the `caddy` package. Key material and users are never deleted: `/etc/vpn-router/pki`, `/etc/vpn-router/ldap`, the user directory in slapd, the
 WireGuard key pair and everything under `/etc/swanctl` are left alone.
 
 ## Building