doc: update nntpd with NNTPS and STARTTLS examples

NNTPS and STARTTLS seems to be working for several months
without incident on news.public-inbox.org, so consider it a
success and maybe others can try using it.

HTTPS technically works, too, but isn't documented at
the moment since I can't recommend production deployments
without varnish protecting it.

2 files changed, 38 insertions, 2 deletions

diff --git a/Documentation/public-inbox-daemon.pod b/Documentation/public-inbox-daemon.pod
index abb84dd7..e8d1ff29 100644
--- a/Documentation/public-inbox-daemon.pod
+++ b/Documentation/public-inbox-daemon.pod
@@ -25,8 +25,6 @@ breaking existing connections during software upgrades.
 These daemons may also utilize multiple pre-forked worker
 processes to take advantage of multiple CPUs.
 
-Native TLS (Transport Layer Security) support is planned.
-
 =head1 OPTIONS
 
 =over
diff --git a/Documentation/public-inbox-nntpd.pod b/Documentation/public-inbox-nntpd.pod
index b56580bf..4214fd75 100644
--- a/Documentation/public-inbox-nntpd.pod
+++ b/Documentation/public-inbox-nntpd.pod
@@ -18,6 +18,44 @@ may be run as a different user than the user running
 L<public-inbox-watch(1)>, L<public-inbox-mda(1)>, or
 L<git-fetch(1)>.
 
+=head1 OPTIONS
+
+See common options in L<public-inbox-daemon(8)/OPTIONS>.
+Additionally, NNTP-specific behavior for certain options
+are supported and documented below.
+
+=over
+
+=item -l, --listen PROTO://ADDRESS/?cert=/path/to/cert,key=/path/to/key
+
+In addition to the normal C<-l>/C<--listen> switch described in
+L<public-inbox-daemon(8)>, the protocol prefix (e.g. C<nntp://> or
+C<nntps://>) may be specified to force a given protocol.
+
+For STARTTLS and NNTPS support, the C<cert> and C<key> may be specified
+on a per-listener basis after a C<?> character and separated by C<,>.
+These directives are per-directive, and it's possible to use a different
+cert for every listener.
+
+=item --cert /path/to/cert
+
+The default TLS certificate for optional STARTTLS and NNTPS support
+if the C<cert> option is not given with C<--listen>.
+
+If using systemd-compatible socket activation and a TCP listener on port
+563 is inherited, it is automatically NNTPS when this option is given.
+When a listener on port 119 is inherited and this option is given, it
+automatically gets STARTTLS support.
+
+=item --key /path/to/key
+
+The default private TLS certicate key for optional STARTTLS and NNTPS
+support if the C<key> option is not given with C<--listen>.  The private
+key may concatenated into the path used by C<--cert>, in which case this
+option is not needed.
+
+=back
+
 =head1 CONFIGURATION
 
 These configuration knobs should be used in the