Ubuntu Manpage: lacme - ACME client written with process isolation and minimal privileges in mind

NAME

       lacme - ACME client written with process isolation and minimal privileges in mind

SYNOPSIS

       lacme [--config=FILENAME] [--socket=PATH] [OPTION ...]  COMMAND [ARGUMENT ...]

DESCRIPTION

lacme is a small ACME client written with process isolation and minimal privileges in mind. It is divid‐
ed into four components, each with its own executable:

1. A lacme-accountd(1) process to manage the account key and issue SHA-256 signatures needed for each
ACME command. (This process binds to a UNIX-domain socket to reply to signature requests from the
ACME client.) One can use the UNIX-domain socket forwarding facility of OpenSSH 6.7 and later to run
lacme-accountd(1) and lacme on different hosts. Alternatively, the lacme-accountd(1) process can be
spawned by the “master” lacme process below; in that case, the two processes communicate through a
socket pair.

2. A “master” lacme process, which runs as root and is the only component with access to the private key
material of the server keys. It is used to fork the ACME client (and optionally the ACME webserver)
after dropping root privileges. For certificate issuances (newOrder command), it also generates Cer‐
tificate Signing Requests, then verifies the validity of the issued certificate, and optionally re‐
loads or restarts services when the notify setting is set.

3. An actual ACME client (specified with the command setting of the [client] section of the configuration
file), which builds ACME commands and dialogues with the remote ACME server. Since ACME commands need
to be signed with the account key, the “master” lacme process passes the lacme-accountd(1) UNIX-domain
socket to the ACME client: data signatures are requested by writing the data to be signed to the sock‐
et.

4. For certificate issuances (newOrder command), an optional webserver (specified with the command set‐
ting of the [webserver] section of the configuration file), which is spawned by the “master” lacme.
(The only challenge type currently supported by lacme is http-01, which requires a webserver to answer
challenges.) That webserver only processes GET and HEAD requests under the /.well-known/acme-chal‐
lenge/ URI. Moreover temporary iptables(8) rules can be automatically installed to open the HTTP
port.

COMMANDS

       lacme account [--tos-agreed] [--register] [CONTACT ...]
              Register (if --registered is set) a lacme-accountd(1)-managed account key.  A list of CONTACT  in‐
              formation  (such  as  maito:  URIs)  can  be specified in order for the ACME server to contact the
              client for issues related to this registration (such as notifications about server-initiated revo‐
              cations).  --tos-agreed indicates agreement with the ACME server’s Terms of Service (and might  be
              required for registration).

              If  the  account key is already registered, update the contact info with the given list of CONTACT
              information.

              Upon success, lacme prints the new or updated Account Object from the ACME server.

       lacme newOrder [--config-certs=FILE] [--min-days=INT|--force] [SECTION ...]
              Read the certificate configuration FILE (see the certificate configuration file section below  for
              the  configuration options), and request new Certificate Issuance for each of its sections (or the
              given list of SECTIONs).  Command alias: new-order.

              The flag --force is an alias for --min-days=-1, which forces renewal regardless of the  expiration
              date of existing certificates.

       lacme revokeCert FILE [FILE ...]
              Request that the given certificate(s) FILE(s) be revoked.  For this command, lacme-accountd(1) can
              be pointed to either the account key or the certificate key.  Command alias: revoke-cert.

GENERIC SETTINGS

       --config=filename
              Use  filename  as  configuration  file  instead  of  %E/lacme/lacme.conf.  The value is subject to
              %-specifier expansion.

              See the configuration file section below for the configuration options.

       --socket=path
              Use path as the lacme-accountd(1) UNIX-domain socket to connect to for signature requests from the
              ACME client.  The value is subject to %-specifier expansion.  lacme aborts if path  exists  or  if
              its parent directory is writable by other users.  Default: %t/S.lacme.

              This command-line option overrides the socket setting of the [client] section of the configuration
              file; it also causes the [accountd] section to be ignored.

       -h, --help
              Display a brief help and exit.

       -q, --quiet
              Be quiet.

       --debug
              Turn on debug mode.

CONFIGURATION FILE

Valid settings are:

DEFAULT SECTION
config-certs
For certificate issuances (newOrder command), specify the space-separated list of certificate con‐
figuration files or directories to use (see the certificate configuration file section below for
the configuration options). Each item in that list is independently subject to %-specifier expan‐
sion.

Paths not starting with / (after %-expansion) are relative to the parent directory of the configu‐
ration filename. The list of files and directories is processed in the specified order, with the
later items taking precedence. Files in a directory are processed in lexicographic order, only
considering the ones with suffix .conf.

Default: lacme-certs.conf lacme-certs.conf.d/.

[client] SECTION
This section is used for configuring the ACME client (which takes care of ACME commands and dialogues
with the remote ACME server).

socket See --socket=.

user The username to drop privileges to (setting both effective and real uid). Skip privilege drop if
the value is empty (not recommended). Default: _lacme-client.

group The groupname to drop privileges to (setting both effective and real gid, and also setting the
list of supplementary gids to that single group). Skip privilege drop if the value is empty (not
recommended). Default: nogroup.

command
The ACME client command. It is split on whitespace, with the first item being the command to exe‐
cute, the second its first argument etc. (Note that lacme might append more arguments when exe‐
cuting the command internally.) Default: /usr/libexec/lacme/client.

server Root URI of the ACME server. Default: https://acme-v02.api.letsencrypt.org/directory.

timeout
Timeout in seconds after which the client stops polling the ACME server and considers the request
failed. Default: 30.

SSL_verify
Whether to verify the server certificate chain. Default: Yes.

SSL_version
Specify the version of the SSL protocol used to transmit data.

SSL_cipher_list
Specify the cipher list for the connection, see ciphers(1ssl) for more information.

[webserver] SECTION
This section is used to configure how ACME challenge responses are served during certificate issuance.

listen Comma- or space-separated list of addresses to listen on. Valid addresses are of the form
IPV4:PORT, [IPV6]:PORT (where the :PORT suffix is optional and defaults to the HTTP port 80), or
an absolute path of a UNIX-domain socket (created with mode 0666). Default: /run/lacme-www.sock‐
et.

Note: The default value is only suitable when an external HTTP daemon is publicly reachable and
passes all ACME challenge requests to the webserver component through the UNIX-domain socket
/run/lacme-www.socket (for instance using the provided /etc/lacme/apache2.conf or /etc/lacme/ng‐
inx.conf configuration snippets for each virtual host requiring authorization). If there is no
HTTP daemon bound to port 80 one needs to set listen to [::] (or 0.0.0.0 [::] when dual IPv4/IPv6
stack is disabled or unavailable), and possibly also set iptables to Yes.

challenge-directory
Directory under which an external HTTP daemon is configured to serve GET requests for challenge
files under /.well-known/acme-challenge/ (for each virtual host requiring authorization) as static
files. The directory must exist beforehand, must be empty, and the lacme client user (by default
_lacme-client) needs to be able to create files under it.

This setting is required when listen is empty. Moreover its value is subject to %-specifier ex‐
pansion before privilege drop.

user The username to drop privileges to (setting both effective and real uid). Skip privilege drop if
the value is empty (not recommended). Default: _lacme-www.

command
The ACME webserver command. It is split on whitespace, with the first item being the command to
execute, the second its first argument etc. (Note that lacme might append more arguments when ex‐
ecuting the command internally.) A separate process is spawned for each address to listen on.
(In particular no webserver process is forked when the listen setting is empty.) Default:
/usr/libexec/lacme/webserver.

iptables
Whether to automatically install temporary iptables(8) rules to open the ADDRESS[:PORT] specified
with listen. The rules are automatically removed once lacme exits. This setting is ignored when
challenge-directory is set. Default: No.

[accountd] SECTION
This section is used for configuring the lacme-accountd(1) child process. If the section (including its
header) is absent or commented out, or if the CLI option --socket is specified, then lacme connects to an
existing lacme-accountd(1) process via the specified UNIX-domain socket.

user The username to drop privileges to (setting both effective and real uid). Skip privilege drop if
the value is empty (the default).

command
The lacme-accountd(1) command. It is split on whitespace, with the first item being the command
to execute, the second its first argument etc. (Note that lacme appends more arguments when exe‐
cuting the command internally.) Each item in that list is independently subject to %-specifier
expansion after privilege drop. Default: /usr/bin/lacme-accountd.

Use for instance `ssh -T lacme@account.example.net lacme-accountd` in order to spawn a remote
lacme-accountd(1) server.

config Path to the lacme-accountd(1) configuration file. Note that the value might be subject to %-ex‐
pansion by lacme-accountd(1).

quiet Be quiet. Possible values: Yes/No.

CERTIFICATE CONFIGURATION FILE

For certificate issuances (newOrder command), a separate file is used to configure paths to the certifi‐
cate and key, as well as the subject, subjectAltName, etc. to generate Certificate Signing Requests.
Each section denotes a separate certificate issuance. Valid settings are:

certificate
Where to store the issued certificate (in PEM format). At least one of certificate or certifi‐
cate-chain is required.

certificate-chain
Where to store the issued certificate along with its chain of trust (in PEM format). At least one
of certificate or certificate-chain is required.

certificate-key
Path to the service’s private key. This setting is required. The genpkey(1ssl) command can be
used to generate a new service RSA key:

$ install -vm0600 /dev/null /path/to/service.rsa.key
$ openssl genpkey -algorithm RSA -out /path/to/service.rsa.key

Alternatively, for an ECDSA key using the NIST P-256 curve:

$ install -vm0600 /dev/null /path/to/service.ecdsa.key
$ openssl genpkey -algorithm EC -out /path/to/service.ecdsa.key \
-pkeyopt ec_paramgen_curve:P-256 \
-pkeyopt ec_param_enc:named_curve

lacme supports any key algorithm than the underlying libssl (OpenSSL) version is able to manipu‐
late, but the ACME server might reject CSRs associated with private keys of deprecated and/or “ex‐
otic” algorithms.

For a dual cert setup (for instance RSA+ECDSA), duplicate the certificate section and use a dis‐
tinct certificate-key resp. certificate (or certificate-chain) value for each key algorithm.

min-days
For an existing certificate, the minimum number of days before its expiration date the section is
considered for re-issuance. A negative value forces reissuance, while the number 0 limits reis‐
suance to expired certificates. Default: the value of the CLI option --min-days, or 21 if there
is no such option.

subject
Subject field of the Certificate Signing Request, in the form /type0=value0/type1=val‐
ue1/type2=.... This setting is required.

subjectAltName
Comma-separated list of Subject Alternative Names, in the form type0:value1,type1:value1,type2:...
The only type currently supported is DNS, to specify an alternative domain name.

CAfile Path to the bundle of trusted issuer certificates. This is used for validating each certificate
after issuance or renewal. Specifying an empty value skips certificate validation. Default:
/usr/share/lacme/ca-certificates.crt.

hash Message digest to sign the Certificate Signing Request with, overriding the req(1ssl) default.

keyUsage
Comma-separated list of Key Usages, for instance digitalSignature, keyEncipherment, to include in
the Certificate Signing Request. See x509v3_config(5ssl) for a list of possible values. Note
that the ACME server might override the value provided here.

tlsfeature
Comma-separated list of TLS extension identifiers, such as status_request for OCSP Must-Staple.
See x509v3_config(5ssl) for a list of possible values. Note that the ACME server might override
the value provided here.

owner, chown
An optional username[:groupname] to chown the issued certificate and certificate-chain to.

mode, chmod
An optional octal mode to chmod the issued certificate and certificate-chain to. By default the
files are created with mode 0644 minus umask restrictions.

notify Command to pass the the system’s command shell (`/bin/sh -c`) after successful installation of the
certificate and/or certificate-chain.

%-SPECIFIERS

       Some  CLI  options  and  configuration  settings are subject to %-expansion for the following specifiers.
       Check the documentation of each setting to see which ones are affected.

       %C       /var/cache for the root  user,  and  $XDG_CACHE_HOME  for  other
                users  (or  $HOME/.cache if the XDG_CACHE_HOME environment vari‐
                able is unset or empty).
       %E       /etc for the root user, and $XDG_CONFIG_HOME for other users (or
                $HOME/.config if the XDG_CONFIG_HOME environment variable is un‐
                set or empty).
       %g       Current group name.
       %G       Current group ID.
       %h       Home directory of the current user.
       %t       /run for the root user, and $XDG_RUNTIME_DIR  for  other  users.
                Non-root users may only use %t when the XDG_RUNTIME_DIR environ‐
                ment variable is set to a non-empty value.
       %T       $TMPDIR,  or /tmp if the TMPDIR environment variable is unset or
                empty.
       %u       Current user name.
       %U       Current user ID.
       %%       A literal %.

EXAMPLES

              $ sudo lacme account --register --tos-agreed mailto:noreply@example.com
              $ sudo lacme newOrder
              $ sudo lacme revokeCert /path/to/service.crt

       Automatic renewal can be scheduled via crontab(5) or systemd.timer(5).  In order  to  avoid  deploying  a
       single  account key onto multiple nodes and/or dealing with multiple account keys, one can install a sin‐
       gle lacme-accountd(1) instance on a dedicated host, generate a single account  key  there  (and  keep  it
       well), and set the following in the [accountd] section:

              command = ssh -T lacme@account.example.net lacme-accountd

       If  the  user running lacme can connect to lacme@account.example.net using (passwordless) key authentica‐
       tion, this setting will spawn a remote lacme-accountd(1) and use it to sign ACME requests.  Further hard‐
       ening can be achieved by means of authorized_keys(5) restrictions:

              restrict,from="...",command="/usr/bin/lacme-accountd --quiet --stdio" ssh-rsa ...

BUGS AND FEEDBACK

       Bugs or  feature  requests  for  lacme  should  be  filed  with  the  Debian  project’s  bug  tracker  at
       <https://www.debian.org/Bugs/>.

AUTHORS

       Guilhem Moulin (mailto:guilhem@fripost.org).

                                                  December 2015                                         lacme(8)