refactor: Generate `saslauthd.conf` via Config Template feature

From a inline config via HereDoc to using a `.tmpl` file that has of all supported keys for SASLAuthd LDAP config.

This additionally supports layering the ENV `.tmpl` generated config over a user-provided config. With a utility method that will ensure earlier duplicate keys are removed.

The two new utilities are documented well enough to grok. `Dockerfile` and `packages.sh` updated to bring in new dependencies and provide the `.tmpl` file.

`log_level` is not documented as a LDAP config key. Original PR did not explain why this key and value chosen were added.

Dockerfile

@@ -120,6 +120,9 @@ COPY \
   target/postfix/ldap-senders.cf \
   /etc/postfix/
 
+# LDAP config support:
+COPY --link target/features/ldap/ /etc/dms/ldap/
+
 # hadolint ignore=SC2016
 RUN <<EOF
   sedfile -i -r 's/^(CRON)=0/\1=1/g' /etc/default/spamassassin

target/features/ldap/saslauthd.tmpl

@@ -0,0 +1,36 @@
+# Parameter docs: https://github.com/cyrusimap/cyrus-sasl/blob/3959d45aa187d906d5fb3e8edf7e3661780967a5/saslauthd/LDAP_SASLAUTHD#L85-L242
+ldap_auth_method: ${LDAP_AUTH_METHOD}
+ldap_bind_dn: ${LDAP_BIND_DN}
+ldap_bind_pw: ${LDAP_BIND_PW}
+ldap_default_domain: ${LDAP_DEFAULT_DOMAIN}
+ldap_default_realm: ${LDAP_DEFAULT_REALM}
+ldap_deref: ${LDAP_DEREF}
+ldap_filter: ${LDAP_FILTER}
+ldap_group_attr: ${LDAP_GROUP_ATTR}
+ldap_group_dn: ${LDAP_GROUP_DN}
+ldap_group_filter: ${LDAP_GROUP_FILTER}
+ldap_group_match_method: ${LDAP_GROUP_MATCH_METHOD}
+ldap_group_search_base: ${LDAP_GROUP_SEARCH_BASE}
+ldap_group_scope: ${LDAP_GROUP_SCOPE}
+ldap_password: ${LDAP_PASSWORD}
+ldap_password_attr: ${LDAP_PASSWORD_ATTR}
+ldap_referrals: ${LDAP_REFERRALS}
+ldap_restart: ${LDAP_RESTART}
+ldap_id: ${LDAP_ID}
+ldap_authz_id: ${LDAP_AUTHZ_ID}
+ldap_mech: ${LDAP_MECH}
+ldap_realm: ${LDAP_REALM}
+ldap_scope: ${LDAP_SCOPE}
+ldap_search_base: ${LDAP_SEARCH_BASE}
+ldap_servers: ${LDAP_SERVERS}
+ldap_start_tls: ${LDAP_START_TLS}
+ldap_time_limit: ${LDAP_TIME_LIMIT}
+ldap_timeout: ${LDAP_TIMEOUT}
+ldap_tls_check_peer: ${LDAP_TLS_CHECK_PEER}
+ldap_tls_cacert_file: ${LDAP_TLS_CACERT_FILE}
+ldap_tls_cacert_dir: ${LDAP_TLS_CACERT_DIR}
+ldap_tls_ciphers: ${LDAP_TLS_CIPHERS}
+ldap_tls_cert: ${LDAP_TLS_CERT}
+ldap_tls_key: ${LDAP_TLS_KEY}
+ldap_use_sasl: ${LDAP_USE_SASL}
+ldap_version: ${LDAP_VERSION}

target/scripts/build/packages.sh

@@ -92,6 +92,18 @@ function _install_packages() {
     "${DEBUG_PACKAGES[@]}"
 }
 
+function _install_feature_config_templates() {
+  _log 'debug' 'Installing support for feature - Config Templates'
+
+  # envsubst:
+  apt-get "${QUIET}" --no-install-recommends install gettext-base
+
+  # zenv:
+  local URL_ZENV="https://github.com/numToStr/zenv/releases/download/0.8.0/zenv-0.8.0-$(uname --machine)-unknown-linux-gnu.tar.gz"
+  # Download from GH releases to stdout, then extract the zenv file to make available via PATH:
+  curl -L "${URL_ZENV}" -o - | tar --gzip --extract --directory /usr/local/bin --file - zenv
+}
+
 function _install_dovecot() {
   declare -a DOVECOT_PACKAGES
 
@@ -219,5 +231,6 @@ _install_rspamd
 _install_fail2ban
 _install_getmail
 _install_utils
+_install_feature_config_templates
 _remove_data_after_package_installations
 _post_installation_steps

target/scripts/helpers/utils.sh

@@ -153,3 +153,39 @@ function _env_var_expect_integer() {
   _log 'warn' "The value of '${ENV_VAR_NAME}' is not an integer ('${!ENV_VAR_NAME}'), but was expected to be"
   return 1
 }
+
+# Ensures that zenv only runs envsubst with ENV filtered from the provided prefix.
+# Those ENV are loaded by zenv in the format of an `.env` file (with prefix dropped by sed)
+# When an ENV is not available, envsubst will evaluate it as empty.
+#
+# @param ${1} = Use a prefix for a group of environment variables
+# @param ${2} = Filepath to ENV template
+# @output     = Template file content populated with available ENV
+function _template_with_env() {
+  local ENV_PREFIX=${1:?ENV prefix is required}
+  local ENV_TEMPLATE=${2:?ENV template filepath is required}
+
+  if [[ ! -f ${ENV_TEMPLATE} ]]; then
+    _dms_panic__invalid_value "file '${ENV_TEMPLATE}' does not exist" 'utils.sh:_use_env_template'
+  fi
+
+  # NOTE: $PATH is retained to avoid needing absolute paths for binaries.
+  env --ignore-environment PATH="${PATH}" \
+    zenv --file <(env | grep "^${ENV_PREFIX}" | sed "s/^${ENV_PREFIX}//") \
+    envsubst < "${ENV_TEMPLATE}"
+}
+
+# Utility to cleanup a config file that may have unset or duplicate keys.
+# - sed => Removes lines where keys have no value assigned.
+# - tac + sort => Remove any duplicate keys (keeps the last instance found).
+#
+# @param ${1} = A delimiter between key and value columns
+# @param ${2} = Input filepath to clean
+# @output     = The transformed file content
+function _cleanse_config() {
+  local KV_DELIMITER=${1:?KV Delimiter is required}
+  local INPUT_FILE=${2?:Input file is required}
+
+  sed "/^[^${KV_DELIMITER}]*${KV_DELIMITER}\s*$/d" ${INPUT_FILE} \
+  | tac | sort -u -t"${KV_DELIMITER}" -k1,1
+}

target/scripts/startup/setup.d/saslauthd.sh

@@ -9,24 +9,7 @@ function _setup_saslauthd() {
   if [[ ${ACCOUNT_PROVISIONER} == 'LDAP' ]] \
   && [[ ! -f /etc/saslauthd.conf ]]; then
     _log 'trace' 'Creating /etc/saslauthd.conf'
-
+    _create_config_saslauthd
-    # Create a config based on ENV
-    sed '/^.*: $/d'> /etc/saslauthd.conf << EOF
-ldap_servers: ${SASLAUTHD_LDAP_SERVER:=${LDAP_SERVER_HOST}}
-ldap_auth_method: ${SASLAUTHD_LDAP_AUTH_METHOD:=bind}
-ldap_bind_dn: ${SASLAUTHD_LDAP_BIND_DN:=${LDAP_BIND_DN}}
-ldap_bind_pw: ${SASLAUTHD_LDAP_PASSWORD:=${LDAP_BIND_PW}}
-ldap_search_base: ${SASLAUTHD_LDAP_SEARCH_BASE:=${LDAP_SEARCH_BASE}}
-ldap_filter: ${SASLAUTHD_LDAP_FILTER:=(&(uniqueIdentifier=%u)(mailEnabled=TRUE))}
-ldap_start_tls: ${SASLAUTHD_LDAP_START_TLS:=no}
-ldap_tls_check_peer: ${SASLAUTHD_LDAP_TLS_CHECK_PEER:=no}
-ldap_tls_cacert_file: ${SASLAUTHD_LDAP_TLS_CACERT_FILE}
-ldap_tls_cacert_dir: ${SASLAUTHD_LDAP_TLS_CACERT_DIR}
-ldap_password_attr: ${SASLAUTHD_LDAP_PASSWORD_ATTR}
-ldap_mech: ${SASLAUTHD_LDAP_MECH}
-ldap_referrals: yes
-log_level: 10
-EOF
   fi
 
   sed -i \
@@ -42,3 +25,20 @@ EOF
 
   gpasswd -a postfix sasl >/dev/null
 }
+
+function _create_config_saslauthd() {
+  local SASLAUTHD_LDAP_SERVER=${SASLAUTHD_LDAP_SERVER:=${LDAP_SERVER_HOST}}
+  local SASLAUTHD_LDAP_BIND_DN=${SASLAUTHD_LDAP_BIND_DN:=${LDAP_BIND_DN}}
+  local SASLAUTHD_LDAP_PASSWORD=${SASLAUTHD_LDAP_PASSWORD:=${LDAP_BIND_PW}}
+  local SASLAUTHD_LDAP_SEARCH_BASE=${SASLAUTHD_LDAP_SEARCH_BASE:=${LDAP_SEARCH_BASE}}
+  local SASLAUTHD_LDAP_FILTER=${SASLAUTHD_LDAP_FILTER:=(&(uniqueIdentifier=%u)(mailEnabled=TRUE))}
+  local SASLAUTHD_LDAP_REFERRALS=${SASLAUTHD_LDAP_REFERRALS:=yes}
+
+  # Generates a config from an ENV template while layering several other sources
+  # into a single temporary file, used as input into `_cleanse_config` which
+  # prepares the final output config.
+  _cleanse_config ':' <(cat 2>/dev/null \
+    /tmp/docker-mailserver/ldap/saslauthd.conf \
+    <(_template_with_env 'SASLAUTHD_' /etc/dms/ldap/saslauthd.tmpl) \
+  ) > /etc/saslauthd.conf
+}