acme-tiny Fedora package

The Fedora package for acme-tiny adds a tiny framework to make issuing and renewing Let's Encrypt certificates convenient. It does not alter your configuration in any way, other than to drop an acme.conf apache config snippet into /etc/httpd/conf.d and provide a systemd service.

If you want a package that tries to do everything for you as root, consider the certbot package.

The ACME protocol will work with other certificate authorities, but acme-tiny is currently hardwired to use letencrypt.org - which is also currently the only ACME certificate authority recognized in most browsers.

These instructions assume you are using letsencrypt for the first time with this acme-tiny package. For example, you should not already have an account key for the domains it will manage. If you do, see README.md for instructions on converting it. Put any existing account key in PEM format in /var/lib/acme/private, readable by the acme user (only!).

The web server must already serve your domains on HTTP

If you cannot access your web domains locally with commands like curl and wget, then this framework won't work. Acme-tiny will work with any web server package, but if you are not using apache (httpd package), you must provide the equivalent of /etc/httpd/conf.d/acme.conf to map /var/www/challenges to the ACME URL location. The web server can even be on a remote machine - provided you have somehow arranged for it to serve files from /var/www/challenges (perhaps via NFS).

If you are using Apache, and restrict access to <location "/">, then this will override the acme.conf global config snippet, and you must explicitly make the ACME URL (http://your.domain.here/.well-known/acme-challenge/) publicly accessible.

Put your CSRs in /var/lib/acme/csr

You can use existing CSRs, or generate a new one using openssl. Put all CSRs to be issued and renewed by acme-tiny in /var/lib/acme/csr. I like to symlink the CSRs into /var/lib/acme/csr, just make sure the acme user can read them (and follow the symlink). The details for openssl are beyond the scope of this documentation, but this should work for creating a certificate for a single domain:

cd /etc/pki/tls
ln -s /var/lib/acme/csr .
openssl req -new -nodes -keyout private/your.domain.key \
    -out csr/your.domain.csr
chmod 0400 private/your.domain.key

If you have an existing key, replace -nodes -keyout with -key. The default openssl config will ask you for data, be sure to give the domain you will be serving when it asks for "Common Name". It is possible to cover multiple domains with a single certificate using openssl. First, add a section to the end of /etc/pki/tls/openssl.cnf defining your extension:

[MYSERV]
subjectAltName=DNS:your.domain,DNS:www.your.domain

Then add -reqexts MYSERV to the openssl command line. One of the domains must match the common name.

Make sure the CSR can be read by the acme user.

Issue the certificate

The timer service in acme-tiny will check the certificate for all CSRs in csr every 24 hours, and issue or renew the certificate if it is missing or about to expire (in 7 days by default). You don't have to wait for the timer, however. Use

systemctl start acme-tiny

to run the service now. The certificate should appear in /var/lib/acme/certs, and errors will be in journalctl. Alternatively (and on EL6), run /usr/libexec/acme-tiny/sign as the acme user, and errors will go to your terminal.

Use the certificate

The default httpd config uses a self-signed localhost certificate for https. Edit /etc/httpd/conf.d/ssl.conf and change SSLCertificateFile and SSLCertificateChainFile to /var/lib/acme/certs/your.domain.crt (or use a symlink to /etc/pki/tls/certs). Change SSLCertificateKeyFile to /etc/pki/tls/private/your.domain.key.

Obviously, you can change the locations to suit your sysadmin tastes.

Some SSL apps, like dovecot, require SSL certificates to be tagged in selinux.

semanage fcontext -a -f 'all files' -t cert_t '/var/lib/acme/certs(/.*)?'
restorecon -rv /var/lib/acme/certs

The above will permanently change the selinux tag to work with dovecot and other apps.

Sendmail is a special problem - it insists that any certificates it loads be only writable by root. This is at odds with the privilege separation of the acme user. (Obviously, the private key must be accessible only by root.) You can, of course, copy the crt file to /etc/pki/tls/certs as root and change the mode. But this has to be done every time the cert is renewed. You can install incron to do this. After installing, create /etc/incron.d/acme with the line

/var/lib/acme/certs/mail.crt IN_MOVED_TO cp $@ /etc/pki/tls/certs

where mail.crt is the certificate sendmail will use. Sendmail can then load it from /etc/pki/tls/certs and be happy. This also solves the file context problem if you add lines for other certificates. You might wonder why we don't simply supply an acme incrontab as part of the package with a wildcard, for example:

/var/lib/acme/certs/*.crt IN_MOVED_TO cp $@ /etc/pki/tls/certs

The answer is that incron is insecure, and very nasty things can be done by putting shell meta characters (including semicolon and quote!) in filenames that then become part of a command run as root. The first example above uses a fixed filename, so that is safe. Complain to incron upstream - they need an option to use a simple execvpe instead of using the shell. Then it would at least be possible to carefully handle malicious names.

Logging and Error Reporting

On EL6, cron will email the acme user when certs are signed or errors are encountered. Under systemd, errors and certs signed are logged with the acme-tiny syslog identifier.

Virtual Hosts

Most web servers can handle multiple logical web hosts - configuring that is beyond the scope of this document. Each virtual host may need to have its own certificate for SSL. They can all share the same key file (see above for how to use an existing key for certificate requests), or use different keys. Put all the CSRs in /var/lib/acme/csr and the acme-tiny service will keep them all renewed. This also works for certificates used by other SSL applications, such as dovecot, sendmail, jabberd, or znc.