some documentation

CHANGELOG

@@ -2,8 +2,13 @@
 This file contains a log of major changes in dehydrated
 
 ## [x.x.x] - xxxx-xx-xx
+## Fixed
+- Various bugfixes around IP certificate orders
+- Implement workaround for OpenSSL regression which broke the time-based validity check
+
 ## Added
 - Added a configuration parameter to allow for timeouts during domain validation processing (`VALIDATION_TIMEOUT`, defaults to 0 = no timeout)
+- Added documentation for IP certificates
 
 ## Changed
 - Only validate existance of wellknown directory or hook script when actually needed

docs/ip-certificates.md

@@ -0,0 +1,97 @@
+## IP Certificates
+
+In addition to issuing certificates for domain names, the ACME protocol also supports certificates
+for IP addresses. Dehydrated has included support for IP identifiers for quite some time, but this
+feature only became practically useful once Let’s Encrypt made IP certificate issuance publicly
+available.
+
+IP certificates can be helpful in scenarios where a service is accessed directly via an address
+rather than a hostname, for example in internal networks, appliances, temporary systems, or
+environments without reliable DNS.
+
+### Limitations and requirements
+
+Currently, there are a few important constraints to be aware of:
+
+- Validation is only possible using http-01 challenges. This means you must have a web server publicly reachable on the IP address you want to certify.
+- Let's Encrypt only issues IP certificates via the shortlived ACME profile. Certificates issued through this profile are currently valid for 7 days.
+
+Because of the short lifetime, it’s important to renew these certificates frequently and adjust
+any automated jobs accordingly.
+
+### Preparing an IP certificate in dehydrated
+
+For convenience, create the certificate directory and a per-certificate configuration file in advance.
+
+Example for an IPv6 address:
+
+```bash
+ip="2001:0db8:0:3::1337"
+```
+
+Or for IPv4:
+
+```bash
+ip="224.13.37.42"
+```
+
+Then set up the certificate directory and configuration and add the ip to domains.txt:
+
+```bash
+# Create certificate directory
+mkdir -p "certs/ip:${ip}"
+
+# Use the shortlived ACME profile for this certificate
+echo "ACME_PROFILE=shortlived" >> "certs/ip:${ip}/config"
+
+# Renew this certificate every 4 days
+echo "RENEW_DAYS=4" >> "certs/ip:${ip}/config"
+
+# Add IP to domains.txt
+echo ip:${ip} >> domains.txt
+```
+
+Keep in mind that you also can use aliases for better readability in your directory structure.
+See the `domains.txt` documentation for more information.
+
+### Requesting the certificate
+
+Once the directory and configuration are in place, you can request and renew the certificate as usual:
+
+```bash
+dehydrated -c
+```
+
+Dehydrated will automatically include the IP identifier and use the configured ACME profile.
+
+### Renewal considerations
+
+Since short-lived certificates expire after one week, make sure that:
+
+- Your renewal job runs frequently enough (for example daily or every few days)
+- Monitoring or alerting accounts for the much shorter validity period
+- Failing to renew in time will result in expired certificates much sooner than with standard domain certificates.
+
+### IPv6 address normalization
+
+To ensure compatibility with Let's Encrypt's seemingly somewhat non-standard handling of IP identifiers,
+dehydrated internally normalizes IPv6 addresses before using them as certificate names.
+
+This process first expands and reformats IPv6 notation into a consistent representation, eliminating
+shorthand forms such as :: compression. Afterwards it re-shortens the IPv6 address in a way that is
+accepted by Let's Encrypt. Doing so guarantees that:
+
+- IPv6 addresses are compatible with Let's Encrypt
+- Matching of existing and configured identifiers works, without dependency on special formatting in domains.txt
+
+This happens internally and should be invisible to most users, but if you are running this against
+a custom ACME server you might want to be aware of this behaviour.
+
+Example formatting:
+
+- Original IPv6 address: `2001:db8:0:3:0:0:0:1337` (not accepted by Let's Encrypt)
+- Fully expanded IPv6 address: `2001:0db8:0000:0003:0000:0000:0000:1337` (also not accepted)
+- Re-shortened IPv6 address: `2001:db8:0:3::1337` (gets accepted)
+
+
+