#!/bin/sh
#
# Purpose {{{
# This script will try to allow SSH connection for a user by
#   1. Getting the username.
#     * Directly from the argument.
#     * Or from an ldap search with a given email address.
#     * Verify that the system knows this user.
#   2. Adding the pubkey to a specific authorized_keys file.
#     * System wide authorized_keys directory (default to /etc/ssh/authorized_keys).
#     * One authorized_keys file per user.
#     * Adding some restriction to the pubkey (allow only scp by default).
# …
#
# 2022-07-19
# }}}
# Vars {{{
PROGNAME=$(basename "${0}"); readonly PROGNAME
PROGDIR=$(readlink -m $(dirname "${0}")); readonly PROGDIR
ARGS="${*}"; readonly ARGS
readonly NBARGS="${#}"
[ -z "${DEBUG}" ] && DEBUG=1
## Export DEBUG for sub-script
export DEBUG

## Default values for some vars
readonly SSH_PUBKEY_FILE_DEFAULT="/tmp/duplicati_id_ed25519.pub"
readonly SSH_PUBKEY_OPTION_DEFAULT='no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty,command="/usr/lib/openssh/sftp-server"'
readonly SSHD_AUTH_KEY_DIR_DEFAULT="/home/.duplicati/ssh/authorized_keys"

## Colors
readonly PURPLE='\033[1;35m'
readonly RED='\033[0;31m'
readonly RESET='\033[0m'
readonly COLOR_DEBUG="${PURPLE}"
# }}}
usage() {                                                       # {{{

	cat <<- HELP
usage: $PROGNAME [-a|-d|-f|-h|-k|-o] -e|-u

This script will try to add a SSH pubkey to allow user's connection.

EXAMPLES :
    - Add default pubkey file (${SSH_PUBKEY_FILE_DEFAULT} to default authorized_keys location (${SSHD_AUTH_KEY_DIR_DEFAULT}) for USERNAME
        ${PROGNAME} --user USERNAME

    - Add pubkey file to a user from the given email address
        ${PROGNAME} --keyfile /tmp/id_ed25519.pub --mail last.name@domain.org

    - Add given pubkey for USERNAME
        ${PROGNAME} --key "ssh-ed25519 AAAAC3NzaC1…" --user USERNAME

    - Add pubkey to specific authorized_keys location
        ${PROGNAME} --user USERNAME --authorized_keys /etc/ssh/authorized_keys

    - Limit "only" port and X11 forwarding on the public key
        ${PROGNAME} --user USERNAME --option "no-port-forwarding,no-X11-forwarding"

OPTIONS :
    -a,--authorized,--authorized_keys
        Set authorized_keys directory to use.
        Default : "${SSHD_AUTH_KEY_DIR_DEFAULT}

    -d,--debug
        Enable debug messages.

    -h,--help
        Print this help message.

    -e,--email,--mail
        Email address to request username with ldapsearch.

    -f,--file,--keyfile
        Path to a file containing the pubkey to allow.
        Default : ${SSH_PUBKEY_FILE_DEFAULT}

    -k,--key
        Complete pubkey with algorithm and the key.
        If not set, fall back to default ssh pubkey file (${SSH_PUBKEY_FILE_DEFAULT} .

    -o,--option
        Options to add to public key. Default basically allow only scp :
        ${SSH_PUBKEY_OPTION_DEFAULT}

    -u,--user,--username
        Username that should have access to the system with the given pubkey.
        If not set, fall back to an LDAP request with email address to guess the username.

HELP

}
# }}}
debug_message() {                                               # {{{

	local_debug_message="${1}"

	## Print message if DEBUG is enable (=0)
	[ "${DEBUG}" -eq "0" ] && printf "${COLOR_DEBUG}%b${RESET}\n" "DEBUG − ${PROGNAME} : ${local_debug_message}"

	unset local_debug_message

	return 0
}
# }}}
error_message() {                                               # {{{

	local_error_message="${1}"
	local_error_code="${2}"

	## Print message
	printf '%b\n' "ERROR − ${PROGNAME} : ${RED}${local_error_message}${RESET}"

	exit "${local_error_code:=66}"
}
# }}}
define_vars() {                                                 # {{{

	## If USER_NAME wasn't defined (argument) {{{
	debug_message "define_vars − \
Check USER related vars."
	if is_var_empty "${USER_NAME}"; then
		if is_var_defined "${USER_EMAIL}"; then
			## Search with email address on the ldap
			debug_message "define_vars − \
Use given email address (${RED}${USER_EMAIL}${COLOR_DEBUG}) to request LDAP server for a matching username."
			USER_NAME="$(ldapsearch -x -ZZ -s one "(mail=${USER_EMAIL})" \
				| awk '/^uid: / { print $2 }')"
			readonly USER_NAME
			is_var_defined "${USER_NAME}" \
				|| error_message "Error with username (${USER_NAME}), please verify the given email address (${USER_EMAIL})." 01
		else
			error_message "Expect USERNAME informations (please use --user or --mail option)." 02
		fi
	fi
	debug_message "define_vars − \
->${RED}${USER_NAME}${COLOR_DEBUG}<- username will be used."
	## }}}
	## If SSHD_AUTH_KEY_DIR wasn't defined (argument) {{{
	debug_message "define_vars − \
Check authorized_keys related var."
	if is_var_empty "${SSHD_AUTH_KEY_DIR}"; then
		SSHD_AUTH_KEY_DIR="${SSHD_AUTH_KEY_DIR_DEFAULT}"
		readonly SSHD_AUTH_KEY_DIR
	fi
	debug_message "define_vars − \
->${RED}${SSHD_AUTH_KEY_DIR}${COLOR_DEBUG}<- directory will be used to store public keys."
	## }}}
	## If SSH_PUBKEY wasn't defined (argument) {{{
	debug_message "define_vars − \
Check SSH_PUBKEY related vars."
	if is_var_empty "${SSH_PUBKEY}"; then
		## Try to get SSH_PUBKEY from SSH_PUBKEY_FILE {{{
		### If SSH_PUBKEY_FILE wasn't defined {{{
		if is_var_empty "${SSH_PUBKEY_FILE}"; then
			### Use default value for SSH_PUBKEY_FILE
			SSH_PUBKEY_FILE="${SSH_PUBKEY_FILE_DEFAULT}"
			readonly SSH_PUBKEY_FILE
		fi
		### }}}
		debug_message "define_vars − \
->${RED}${SSH_PUBKEY_FILE}${COLOR_DEBUG}<- file will be used to provide user's public key."
		### If SSH_PUBKEY_FILE doesn't exists {{{
		#### AND Exit with error
		is_file_absent "${SSH_PUBKEY_FILE}" \
			&& error_message "Error, public key file (${SSH_PUBKEY_FILE}) doesn't exists (please check --keyfile option)." 03
		### }}}
		SSH_PUBKEY="$(grep --max-count=1 -- "ssh-" "${SSH_PUBKEY_FILE}" \
			|| error_message "Error, can't retrieve ssh pubkey content from pubkey file (${SSH_PUBKEY_FILE}" 04)"
		### }}}
	fi
	# Can't use default debug_message function due to some limitations (size ?)
	if [ "${DEBUG}" -eq "0" ]; then
		printf "${COLOR_DEBUG}%b${RESET}\n" "DEBUG − ${PROGNAME} : define_vars − ->"
		printf "${RED}%b${RESET}\n" "${SSH_PUBKEY}"
		printf "${COLOR_DEBUG}%b${RESET}\n" "<- key will be used as user's public key."
	fi
	## }}}
	## If SSH_PUBKEY_OPTION wasn't defined (argument) {{{
	debug_message "define_vars − \
Check ssh_pubkey OPTIONS related var."
	if is_var_empty "${SSH_PUBKEY_OPTION}"; then
		### Use default value for SSH_PUBKEY_OPTION
		SSH_PUBKEY_OPTION="${SSH_PUBKEY_OPTION_DEFAULT}"
		readonly SSH_PUBKEY_OPTION
	fi
		debug_message "define_vars − \
->${RED}${SSH_PUBKEY_OPTION}${COLOR_DEBUG}<- options will be used for public key."
	## }}}

}
# }}}
is_var_defined() {                                              # {{{

	## Test if at least one of the given var(s) is defined

	## Return False by default
	return_var_defined="1"
	## Total number of variables to test
	local_total_var="${#}"

	loop_count_var_defined="0"

	## While it remains a variable to test
	while [ "${local_total_var}" -gt "${loop_count_var_defined}" ]; do
		debug_message "is_var_defined − \
Test var: ${1}."
		### Test if this is defined and set return value to True
		[ -n "${1}" ] && return_var_defined="0"

		### Increase the number of tested variables
		loop_count_var_defined=$((loop_count_var_defined+1))

		### Shift to the next variable
		shift
	done

	unset local_total_var
	unset loop_count_var_defined

	return "${return_var_defined}"
}
# }}}
is_var_empty() {                                                # {{{

	## Test if at least one of the given var(s) is empty

	## Return False by default
	return_var_empty="1"
	## Total number of variables to test
	local_total_var="${#}"

	loop_count_var_empty="0"

	## While it remains a variable to test
	while [ "${local_total_var}" -gt "${loop_count_var_empty}" ]; do
		debug_message "is_var_empty − \
Test var: ${1}."
		### Test if this is empty and set return value to True
		[ -z "${1}" ] && return_var_empty="0"

		### Increase the number of tested variables
		loop_count_var_empty=$((loop_count_var_empty+1))

		### Shift to the next variable
		shift
	done

	unset local_total_var
	unset loop_count_var_defined

	return "${return_var_empty}"
}
# }}}
is_directory_absent() {                                         # {{{

	local_directory_absent="${1}"

	## Directory doesn't exists by default
	return_is_directory_absent="0"

	### Check if the directory exists
	# shellcheck disable=SC2086
	if test -d "${local_directory_absent}"; then
		return_is_directory_absent="1"
		debug_message "is_directory_absent − \
The directory ${RED}${local_directory_absent}${COLOR_DEBUG} exists."
	else
		return_is_directory_absent="0"
		debug_message "is_directory_absent − \
The directory ${RED}${local_directory_absent}${COLOR_DEBUG} doesn't exist."
	fi

	return "${return_is_directory_absent}"

}
# }}}
is_file_absent() {                                              # {{{

	local_file_absent="${1}"

	## File exists by default
	return_is_file_absent="1"

	### Check if the file exists
	# shellcheck disable=SC2086
	if find ${local_file_absent} > /dev/null 2>&1; then
		return_is_file_absent="1"
		debug_message "is_file_absent − \
The file ${RED}${local_file_absent}${COLOR_DEBUG} exists."
	else
		return_is_file_absent="0"
		debug_message "is_file_absent − \
The file ${RED}${local_file_absent}${COLOR_DEBUG} doesn't exist."
	fi

	return "${return_is_file_absent}"

}
# }}}

main() {                                                        # {{{

	## Define all vars
	define_vars

	## Check if user exists {{{
	if id -u "${USER_NAME}" >/dev/null 2>&1; then
		debug_message "main − \
The user ${RED}${USER_NAME}${COLOR_DEBUG} was found on the system."
	else
		### OR Exit with error message
		error_message "According to given informations the user (${USER_NAME}) wasn't found on this system.\nPlease check the value passed to --user or --mail options." 11
	fi
	## }}}
	## Manage authorized_keys file {{{
	USER_AUTHORIZED_KEYS_FILE="${SSHD_AUTH_KEY_DIR}/${USER_NAME}"
	## Ensure authorized_keys directory exists {{{
	if is_directory_absent "${SSHD_AUTH_KEY_DIR}"; then
		debug_message "main − \
Create authorized_keys directory (${RED}${SSHD_AUTH_KEY_DIR}${COLOR_DEBUG})."
		mkdir --parents -- "${SSHD_AUTH_KEY_DIR}" \
			|| error_message "Error when creating authorized_keys directory (${SSHD_AUTH_KEY_DIR})." 21
	fi
	## }}}
	## Ensure user's authorized_keys file exists {{{
	if is_file_absent "${USER_AUTHORIZED_KEYS_FILE}"; then
		debug_message "main − \
Create authorized_keys file for ${USER_NAME} (${RED}${USER_AUTHORIZED_KEYS_FILE}${COLOR_DEBUG})."
		touch -- "${USER_AUTHORIZED_KEYS_FILE}" \
			|| error_message "Error when creating ${USER_NAME}'s authorized_keys file (${USER_AUTHORIZED_KEYS_FILE})." 22
	fi
	## }}}
	## }}}
	## If pubkey is already in authorized_keys file {{{
	##      --fixed-strings to be able to manage backslash
	### AND Ensure it's set with the right options
	### AND Exit the script
	if grep --fixed-strings --word-regexp --quiet -- "${SSH_PUBKEY}" "${USER_AUTHORIZED_KEYS_FILE}"; then
		sed -i "s|.*${SSH_PUBKEY}.*|${SSH_PUBKEY_OPTION} ${SSH_PUBKEY}|" "${USER_AUTHORIZED_KEYS_FILE}" \
			|| error_message "Error during SSH_PUBKEY replacement with expected options in authorized_keys file (${USER_AUTHORIZED_KEYS_FILE})." 31
		debug_message "The given pubkey was already present in authorized_keys file (${RED}${USER_AUTHORIZED_KEYS_FILE}${COLOR_DEBUG}) and now have the expected permissions."
	## }}}
	## If pubkey isn't already in authorized_keys file {{{
	### Add it with expected options
	else
		printf "%s" "${SSH_PUBKEY_OPTION} ${SSH_PUBKEY}" >> "${USER_AUTHORIZED_KEYS_FILE}" \
			|| error_message "Error while adding SSH_PUBKEY with expected options in authorized_keys file (${USER_AUTHORIZED_KEYS_FILE})." 32
		debug_message "The given pubkey is now present in authorized_keys file (${RED}${USER_AUTHORIZED_KEYS_FILE}${COLOR_DEBUG}) with expected permissions."
	fi
	## }}}
	## If the key is present, exit with success {{{
	##      --fixed-strings to be able to manage backslash
	if grep --fixed-strings --word-regexp --quiet -- "${SSH_PUBKEY_OPTION} ${SSH_PUBKEY}" "${USER_AUTHORIZED_KEYS_FILE}"; then
		printf "%b" "The given pubkey (${RED}${SSH_PUBKEY_FILE}${RESET}) for ${RED}${USER_NAME}${RESET} user was successfully added to it's authorized_keys file (${RED}${USER_AUTHORIZED_KEYS_FILE}${COLOR_DEBUG})." \
			&& exit 0
	else
		error_message "Error with verification of user authorized_keys content (${USER_AUTHORIZED_KEYS_FILE}). Can't detect the new SSH_PUBKEY." 33
	fi

	## }}}
}
# }}}

# Manage arguments                                                # {{{
# This code can't be in a function due to argument management

if [ ! "${NBARGS}" -eq "0" ]; then

	manage_arg="0"

	## If the first argument is not an option
	if ! printf -- '%s' "${1}" | grep -q -E -- "^-+";
	then
		## Print help message and exit
		printf '%b\n' "${RED}Invalid option: ${1}${RESET}"
		printf '%b\n' "---"
		usage

		exit 1
	fi

	# Parse all options (start with a "-") one by one
	while printf -- '%s' "${1}" | grep -q -E -- "^-+"; do

	case "${1}" in
		-a|--authorized_keys|--authorized )   ## Define SSHD_AUTH_KEY_DIR with given arg
			## Move to the next argument
			shift
			## Define var
			readonly SSHD_AUTH_KEY_DIR="${1}"
			;;
		-d|--debug )                          ## debug
			DEBUG=0
			;;
		-h|--help )                           ## help
			usage
			## Exit after help informations
			exit 0
			;;
		-e|--email|--mail )                   ## Define USER_EMAIL with given arg
			## Move to the next argument
			shift
			## Define var
			readonly USER_EMAIL="${1}"
			;;
		-f|--file|--keyfile )                 ## Define SSH_PUBKEY_FILE with given arg
			## Move to the next argument
			shift
			## Define var
			readonly SSH_PUBKEY_FILE="${1}"
			;;
		-o|--option|--options )               ## Define SSH_PUBKEY_OPTION with given arg
			## Move to the next argument
			shift
			## Define var
			readonly SSH_PUBKEY_OPTION="${1}"
			;;
		-k|--key )                            ## Define SSH_PUBKEY with given arg
			## Move to the next argument
			shift
			## Define var
			readonly SSH_PUBKEY="${1}"
			;;
		-u|--user|--username )                ## Define USER_NAME with given arg
			## Move to the next argument
			shift
			## Define var
			readonly USER_NAME="${1}"
			;;
		* )                                   ## unknow option
			printf '%b\n' "${RED}Invalid option: ${1}${RESET}"
			printf '%b\n' "---"
			usage
			exit 1
			;;
	esac

	debug_message "Arguments management − \
${RED}${1}${COLOR_DEBUG} option managed."

	## Move to the next argument
	shift
	manage_arg=$((manage_arg+1))

	done

	debug_message "Arguments management − \
${RED}${manage_arg}${COLOR_DEBUG} argument(s) successfully managed."
else
	debug_message "Arguments management − \
No arguments/options to manage."
fi

# }}}

# Call main
main

# The script should never reach this line
error_message "Unexpected end of the script, please use '--debug' option to have more informations" 255