ACME-CLIENT(1)

NAME
acme-client - ACME client

SYNOPSIS
acme-client [-Fnrv] [-f configfile] [-e keyid:key] handle

DESCRIPTION
acme-client is an Automatic Certificate Management Environment (ACME) client: it looks in its configuration for a domain section corresponding to the handle given as command line argument and uses that configuration to retrieve an X.509 certificate which can be used to provide domain name validation (i.e. prove that the domain is who it says it is). The certificates are typically used to provide HTTPS for web servers, but can be used in any situation where domain name validation is required (such as mail servers).

If the certificate already exists and is close to expiry, acme-client attempts to renew the certificate. For certificates with a lifetime of more than 10 days, this is done when less than a third of the lifetime remains. Otherwise, renewal is done when half the lifetime has expired.

In order to prove that the client has access to the domain, a challenge is issued by the signing authority. acme-client implements the “http-01” challenge type, where a file is created within a directory accessible by a locally run web server. The default challenge directory /var/www/acme can be served by httpd(8) with this location block, which will properly map response challenges:

    location "/.well-known/acme-challenge/*" {
    	root "/acme"
    	request strip 2
    }

Some signing authorities require the client to perform external account binding to associate the ACME account key generated by acme-client with an existing account in a non-ACME system such as a CA customer database. To enable ACME account binding, the CA operating the ACME server needs to provide the ACME client with a base64url-encoded MAC key and a key identifier string, using some mechanism outside of ACME. These can be supplied to acme-client using the -e command line argument.

The options are as follows:

-F  Force certificate renewal, regardless of remaining lifetime.

-e key-id:key
    Specify external account binding parameters. This consists of the key identifier string and the base64url-encoded MAC key separated by a colon.

-f configfile
    Specify an alternative configuration file.

-n  No operation: check and print configuration.

-r  Revoke the X.509 certificate.

-v  Verbose operation. Specify twice to also trace communication and data transfers.

handle
    The handle of the domain section of the configuration that contains the details of the certificate to be created, renewed or revoked.

FILES
/etc/acme
    Private keys for acme-client.
/etc/acme-client.conf
    Default configuration.
/var/www/acme
    Default challengedir.

EXIT STATUS
acme-client returns 0 if certificates were changed (revoked or updated), 1 on failure, or 2 if the certificates didn't change (up to date).

EXAMPLES
Example configuration files for acme-client and httpd(8) are provided in /etc/examples/acme-client.conf and /etc/examples/httpd.conf.

To generate a certificate for example.com and use it to provide HTTPS, create acme-client.conf and httpd.conf and run:

    # acme-client -v example.com && rcctl reload httpd

A cron(8) job can renew the certificate as necessary. On renewal, httpd(8) is reloaded:

    ~ * * * * acme-client example.com && rcctl reload httpd

SEE ALSO
openssl(1), acme-client.conf(5), httpd.conf(5), ssl(8)

STANDARDS
R. Barnes, J. Hoffman-Andrews, D. McCarney, J. Kasten, March 2019, RFC 8555, Automatic Certificate Management Environment (ACME).

HISTORY
The acme-client utility first appeared in OpenBSD 6.1.

AUTHORS
The acme-client utility was written by Kristaps Dzonsons <kristaps@bsd.lv>.

CAVEATS
The usual ACME service providers are notoriously picky about authenticating rules, and yield fairly long time-outs after just a few invalid attempts. It is strongly suggested to first validate a configuration with a staging server before moving an official certificate validation workflow to crontab(5) status.