2.5 KiB
Cert Spotter
Cert Spotter is a tool for monitoring Certificate Transparency logs.
Service Configuration
A basic config that notifies you of all certificate changes for your domain would look as follows:
services.certspotter = {
enable = true;
# replace example.org with your domain name
watchlist = [ ".example.org" ];
emailRecipients = [ "webmaster@example.org" ];
};
# Configure an SMTP client
programs.msmtp.enable = true;
# Or you can use any other module that provides sendmail, like
# services.nullmailer, services.opensmtpd, services.postfix
In this case, the leading dot in ".example.org" means that Cert
Spotter should monitor not only example.org, but also all of its
subdomains.
Operation
By default, NixOS configures Cert Spotter to skip all certificates
issued before its first launch, because checking the entire
Certificate Transparency logs requires downloading tens of terabytes of
data. If you want to check the entire logs for previously issued
certificates, you have to set services.certspotter.startAtEnd to
false and remove all previously saved log state in
/var/lib/certspotter/logs. The downloaded logs aren't saved, so if you
add a new domain to the watchlist and want Cert Spotter to go through
the logs again, you will have to remove /var/lib/certspotter/logs
again.
After catching up with the logs, Cert Spotter will start monitoring live logs. As of October 2023, it uses around 20 Mbps of traffic on average.
Hooks
Cert Spotter supports running custom hooks instead of (or in addition to) sending emails. Hooks are shell scripts that will be passed certain environment variables.
To see hook documentation, see Cert Spotter's man pages:
nix-shell -p certspotter --run 'man 8 certspotter-script'
For example, you can remove emailRecipients and send email
notifications manually using the following hook:
services.certspotter.hooks = [
(pkgs.writeShellScript "certspotter-hook" ''
function print_email() {
echo "Subject: [certspotter] $SUMMARY"
echo "Mime-Version: 1.0"
echo "Content-Type: text/plain; charset=US-ASCII"
echo
cat "$TEXT_FILENAME"
}
print_email | ${config.services.certspotter.sendmailPath} -i webmaster@example.org
'')
];