Certificate export, missing PTR list, simpler "Used for"

- Certificates can be exported for use outside Jarl: Export… on the
  Certificates page (download or copy), jarl cert export, and
  GET /certificates/{name}/pem?part=fullchain|cert|key|bundle.
  Administrators only; key exports are audited.
- A reverse zone's missing-PTR banner lists the addresses and names
  (ptr_missing_list in the zone API).
- "Used for" shows DoT/DoH for named, and "not used by Jarl" instead of
  "nothing yet".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/api.md

@@ -604,6 +604,7 @@ Administrators only. See [certificates.md](certificates.md#api).
 | GET, PATCH, DELETE | `/certificates/{name}` | |
 | POST | `/certificates/{name}/issue` | 202: being obtained (poll until `issuing_since` is gone); a file certificate is reread (200) |
 | POST | `/certificates/{name}/check` | the routes of a certificate's names |
+| GET | `/certificates/{name}/pem?part=PART` | the certificate as PEM: `fullchain` (default), `cert`, `key`, `bundle`; key exports audited ([certificates.md](certificates.md#using-a-certificate-outside-jarl)) |
 
 `GET /status` includes `certificates` for administrators: `total`,
 `problems` (failing, expiring, expired), `next` and `next_after`,

docs/certificates.md

@@ -216,11 +216,35 @@ and the last good one stays in use. jarld runs as user `jarl`, which must
 be able to read both files (e.g. `chgrp jarl` and `chmod 640`, or have
 your renewal hook copy them somewhere it can read).
 
+## Using a certificate outside Jarl
+
+A certificate needn't be used by Jarl at all ("not used by Jarl" on the
+Certificates page): Jarl obtains and renews it, and you export it for
+another program, such as a mail server or a reverse proxy. **Export…** on
+the Certificates page downloads each file or copies it to the clipboard
+(copying needs the web UI over HTTPS, or from localhost). Or:
+
+```sh
+jarl cert export mail --dir /etc/ssl/mail             # fullchain.pem, and privkey.pem (mode 600)
+jarl cert export mail --part bundle > /etc/haproxy/mail.pem
+```
+
+The parts are `fullchain` (the certificate and its chain), `cert` (the
+certificate alone), `key` and `bundle` (the key, then the chain, in one
+file, as HAProxy wants). Only administrators can export, and every export
+of the key is in the audit log (`certificate.export_key`).
+
+Jarl renews the certificate, not your copy: export it again after each
+renewal (`jarl cert show` says when that is), for example from a daily
+cron job. A program on this server can instead read the files Jarl writes
+for named (use `dns`), which Jarl keeps current.
+
 ## Security notes
 
 - Certificates Jarl obtains, their keys and the ACME account key are kept
   in Jarl's database, so they are in its backups (like TSIG secrets). The
-  API never returns a key.
+  API returns a key only to an administrator who exports it, and records
+  that in the audit log.
 - Every publicly trusted certificate is published in Certificate
   Transparency logs, with all its names. A name like `ns1.adbraun.lol`
   used for both the web UI and DNS reveals less than separate names. Avoid
@@ -240,6 +264,7 @@ your renewal hook copy them somewhere it can read).
 | GET, PATCH, DELETE | `/certificates/{name}` | `domains` and `uses` replace the whole list |
 | POST | `/certificates/{name}/issue` | obtain now: 202, then poll `GET /certificates/{name}` until `issuing_since` is gone; a file certificate is reread (200) |
 | POST | `/certificates/{name}/check` | the routes for an existing certificate |
+| GET | `/certificates/{name}/pem?part=fullchain` | the certificate as PEM, to save: `fullchain` (default), `cert`, `key` or `bundle` (key and chain). Exports of the key are audited |
 
 ## Testing with Pebble
 

docs/cli.md

@@ -446,6 +446,8 @@ jarl cert show ns1
 jarl cert issue ns1                                  # renew now (--no-wait to return at once)
 jarl cert update ns1 --challenge porkbun             # auto, jarl or porkbun
 jarl cert update ns1 --use dns                       # --use and --domain replace the list (--use none)
+jarl cert export mail --dir /etc/ssl/mail            # fullchain.pem and privkey.pem, for another program
+jarl cert export mail --part bundle                  # one part to stdout: fullchain, cert, key, bundle
 jarl cert delete ns1
 jarl cert account                                    # the ACME account (set in jarl.yaml)
 ```

docs/reverse.md

@@ -132,8 +132,10 @@ view's A and AAAA records use. An address with several names gets one PTR:
 3. the shortest name, then the first alphabetically.
 
 Jarl says which name it chose, and which it didn't, so you can change it.
-A reverse zone's page shows how many addresses still lack a PTR, with a
-button to add them. `jarl zone show` shows it as `Missing PTRs`.
+A reverse zone's page shows the addresses that still lack a PTR record and
+the name each would get (the first 25), with a button to add them. `jarl
+zone show` shows how many as `Missing PTRs`; the API lists them in
+`ptr_missing_list`.
 
 ## Keeping PTR records in step