fix ipps certificate lookup

openspec/changes/fix-ipps-certificate-lookup/specs/printserver/cups/spec.md

@@ -0,0 +1,41 @@
+# Spec Delta
+
+## MODIFIED Requirements
+
+### Requirement: Secure AirPrint certificate matches the advertised name
+The container SHALL serve the secure `_ipps` (TLS) service with a certificate
+whose subject alternative names cover the names clients use to reach it, so
+clients that validate the name complete the secure connection instead of falling
+back to a generic driver.
+
+#### Scenario: Certificate is created on first start
+- **WHEN** the container starts and no certificate is present in the certificate directory
+- **THEN** a self-signed certificate and key are generated whose subject alternative names cover the container host name, its `<host name>.local` form, the name Avahi advertises, `localhost`, `localhost.localdomain`, `host.containers.internal` and `127.0.0.1`
+
+#### Scenario: Additional names are accepted
+- **WHEN** the container is started with `CERT_EXTRA_NAMES` set to a comma-separated list of DNS names and/or IP addresses
+- **THEN** every listed name is included as a subject alternative name of the generated certificate
+
+#### Scenario: Validity is configurable
+- **WHEN** the container is started with `CERT_DAYS`
+- **THEN** the generated certificate is valid for that number of days
+
+#### Scenario: An existing certificate is reused
+- **WHEN** the container starts and the existing certificate already covers every required name
+- **THEN** it is kept instead of reissued, so clients that trusted it do not have to trust a new certificate
+
+#### Scenario: Missing names trigger reissue
+- **WHEN** the container starts and a required name — for example a newly added `CERT_EXTRA_NAMES` entry — is not covered by the existing certificate
+- **THEN** a certificate covering it is generated
+
+#### Scenario: CUPS presents the certificate
+- **WHEN** a client connects over `_ipps` to the name Avahi advertises
+- **THEN** the certificate CUPS presents contains that name in its subject alternative names
+
+#### Scenario: Certificate is served for the connecting address
+- **WHEN** a client connects over `_ipps` to one of the host's addresses — for example its LAN address or an IPv6 address — rather than to the advertised name
+- **THEN** CUPS presents the container's certificate, so the names in its subject alternative names (including the advertised name) still apply
+
+#### Scenario: A validating client must trust the certificate
+- **WHEN** a client validates the certificate chain
+- **THEN** the connection is rejected until the self-signed certificate is trusted on the client, while the plain `_ipp` service keeps working