Split run.sh and add git retrival

This patch modularize run.sh, adding two new helper scripts and
make it possible to specify a git repository for ssh keys via a
new env variable `BORG_SSHKEYS_REPO`.

the modularization add two new files :
- `env.sh` : define a few envriroment variables
- `create-client-dirs.sh`  : update and create user directories and
  re-create authorized_keys

We also add a new script `update-ssh-keys.sh` to be called regurlarly
in a cron job to check if the git repository is up-to-date and
eventually adding/removing users.

data/create-client-dirs.sh

@@ -0,0 +1,66 @@
+#!/bin/bash
+
+set -e
+
+source env.sh
+
+function error_exit {
+    echo
+    echo "$@"
+    if [ -e "${AUTHORIZED_KEYS_PATH}.bkp" ]; then
+      echo "Restore authorized_keys backup ${AUTHORIZED_KEYS_PATH}.bkp"
+      mv "${AUTHORIZED_KEYS_PATH}.bkp" "${AUTHORIZED_KEYS_PATH}"
+    fi
+    exit 1
+}
+
+#Trap the killer signals so that we can exit with a good message.
+trap "error_exit 'Received signal SIGHUP'" SIGHUP
+trap "error_exit 'Received signal SIGINT'" SIGINT
+trap "error_exit 'Received signal SIGTERM'" SIGTERM
+
+echo "######################################################"
+echo "* Regenerate borgserver authorized_keys *"
+echo "######################################################"
+
+if [ -e "${AUTHORIZED_KEYS_PATH}" ]; then
+  cp "${AUTHORIZED_KEYS_PATH}" "${AUTHORIZED_KEYS_PATH}.bkp"
+  rm "${AUTHORIZED_KEYS_PATH}"
+fi
+
+# Add every key to borg-users authorized_keys
+for keyfile in $(find "${SSH_KEY_DIR}/clients" ! -regex '.*/\..*' -a -type f); do
+  client_name=$(basename ${keyfile})
+  echo "Add $client_name ssh key"
+  if [ ! -d "${BORG_DATA_DIR}/${client_name}" ]; then
+    mkdir "${BORG_DATA_DIR}/${client_name}" #2>/dev/null
+    echo "  ** Adding client ${client_name} with repo path ${BORG_DATA_DIR}/${client_name}"
+  else
+    echo "Directory ${BORG_DATA_DIR}/${client_name} exists: Nothing to do"
+  fi
+
+  # If client is $BORG_ADMIN unset $client_name, so path restriction equals $BORG_DATA_DIR
+  # Otherwise add --append-only, if enabled
+  borg_cmd=${BORG_CMD}
+  if [ "${client_name}" == "${BORG_ADMIN}" ] ; then
+    echo "   ** Client '${client_name}' is BORG_ADMIN! **"
+    unset client_name
+  elif [ "${BORG_APPEND_ONLY}" == "yes" ] ; then
+    borg_cmd="${BORG_CMD} --append-only"
+  fi
+
+  echo -n "command=\"$(eval echo -n \"${borg_cmd}\")\" " >> ${AUTHORIZED_KEYS_PATH}
+  cat ${keyfile} >> ${AUTHORIZED_KEYS_PATH}
+done
+
+echo " * Validating structure of generated ${AUTHORIZED_KEYS_PATH}..."
+ERROR=$(ssh-keygen -lf ${AUTHORIZED_KEYS_PATH} 2>&1 >/dev/null)
+if [ $? -ne 0 ]; then
+    echo "ERROR: ${ERROR}"
+    exit 1
+fi
+
+chown -R borg:borg ${BORG_DATA_DIR}
+chown borg:borg ${AUTHORIZED_KEYS_PATH}
+chmod 600 ${AUTHORIZED_KEYS_PATH}
+rm -f ${AUTHORIZED_KEYS_PATH}.bkp