#! /usr/bin/python
#
# ssh-import-id - Authorize SSH public keys from trusted online identities
#
# Copyright (c) 2013 Casey Marshall <casey.marshall@gmail.com>
# Copyright (c) 2013 Dustin Kirkland <dustin.kirkland@gmail.com>
#
# ssh-import-id is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, version 3.
#
# ssh-import-id is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with ssh-import-id.  If not, see <http://www.gnu.org/licenses/>.

import argparse
import logging
import os
import stat
import subprocess
import sys
import tempfile

DEFAULT_PROTO = "lp"

logging.basicConfig(format='%(asctime)s %(levelname)s %(message)s', level=logging.INFO)

parser = argparse.ArgumentParser(description='Authorize SSH public keys from trusted online identities.')
parser.add_argument('-o', '--output', metavar='FILE', help='Write output to file (default ~/.ssh/authorized_keys)')
parser.add_argument('-r', '--remove', help='Remove a key from authorized keys file', action="store_true", default=False)
parser.add_argument('userids', nargs='+', metavar="USERID", help='User IDs to import')
parser.options = None

TEMPFILES = []


def cleanup():
	"""
	Cleanup tempfiles
	"""
	for f in TEMPFILES:
		if os.path.exists(f):
			os.unlink(f)


def die(msg):
	"""
	The only thing in Perl worth keeping
	"""
	logging.error(msg)
	cleanup()
	os._exit(1)


def key_fingerprint(fields):
	"""
	Get the fingerprint for an SSH public key
	Returns None if not valid key material
	"""
	if not fields:
		return None
	if len(fields) < 3:
		return None
	tempfd, tempname = tempfile.mkstemp(prefix='ssh-auth-key-check', suffix='.pub')
	TEMPFILES.append(tempname)
	with os.fdopen(tempfd, "w") as tempf:
		tempf.write(" ".join(fields))
		tempf.write("\n")
	keygen_proc = subprocess.Popen(['ssh-keygen', '-l', '-f', tempname], stdout=subprocess.PIPE)
	keygen_out, _ = keygen_proc.communicate(None)
	if keygen_proc.returncode:
		# Non-zero RC: probably not a public key
		return None
	os.unlink(tempname)
	keygen_fields = keygen_out.split()
	if not keygen_fields or len(keygen_fields) < 2:
		# Empty output?
		return None
	out = []
	for k in keygen_out.split():
		out.append(str(k.decode('utf-8').strip()))
	return out


def open_output(name, mode='a+'):
	"""
	Open output for writing, supporting either stdout or a filename
	"""
	if name == '-':
		return False
	else:
		return open(name, mode)


def assert_parent_dir(keyfile):
	"""
	Ensure that the keyfile parent directory exists
	"""
	# Standard out: nothing to do
	if keyfile == "-":
		return True
	# Get output file parent directory
	if os.path.dirname(keyfile):
		parent_dir = os.path.dirname(keyfile)
	else:
		parent_dir = "."
	# Ensure parent directory exists
	if not os.path.exists(parent_dir):
		umask = os.umask(0o077)
		os.makedirs(parent_dir, 0o700)
		os.umask(umask)
	if os.path.isdir(parent_dir):
		return True
	else:
		die("Parent directory not found for output [%s]" % (keyfile))
	return False


def read_keyfile():
	"""
	Locate key file, read the current state, return lines in a list
	"""
	lines = []
	output_file = parser.options.output or os.path.join(os.getenv("HOME"), ".ssh", "authorized_keys")
	if os.path.exists(output_file):
		try:
			with open(output_file, "r") as f:
				lines = f.readlines()
		except:
			die("Could not read authorized key file [%s]" % (output_file))
	return lines


def write_keyfile(keyfile_lines, mode):
	"""
	Locate key file, write lines to it
	"""
	output_file = parser.options.output or os.path.join(os.getenv("HOME"), ".ssh", "authorized_keys")
	if output_file == "-":
		for line in keyfile_lines:
			if line:
				sys.stdout.write(line)
				sys.stdout.write("\n")
		sys.stdout.flush()
	elif assert_parent_dir(output_file):
		with open(output_file, mode) as f:
			for line in keyfile_lines:
				if line.strip():
					f.write(line)
					f.write("\n")


def fp_tuple(fp):
	"""
	Build a string that uniquely identifies a key
	"""
	# An SSH public key is uniquely identified by the tuple [length, hash, type]]
	# fp should be a list of results of the `ssh-keygen -l -f` command
	return ' '.join([fp[0], fp[1], fp[-1]])


def key_list(keyfile_lines):
	"""
	Return a list of uniquely identified keys
	"""
	# Map out which keys we already have
	keys = []
	for line in keyfile_lines:
		ssh_fp = key_fingerprint(line.split())
		if ssh_fp:
			keys.append(fp_tuple(ssh_fp))
	logging.debug("Already have SSH public keys: [%s]" % (' '.join(keys)))
	return keys


def fetch_keys(proto, username):
	"""
	Call out to a subcommand to handle the specified protocol and username
	"""
	proto_cmd_path = os.path.join(os.path.dirname(sys.argv[0]), "%s-%s" % (os.path.basename(sys.argv[0]), proto))
	if not os.path.isfile(proto_cmd_path) or not os.access(proto_cmd_path, os.X_OK):
		die("ssh-import-id protocol handler %s: not found or cannot execute" % (proto_cmd_path))
	proc = subprocess.Popen([proto_cmd_path, username], stdout=subprocess.PIPE)
	output, _ = proc.communicate(None)
	if proc.returncode:
		raise Exception("Error executing protocol helper [%s]" % proto_cmd_path)
	return output.split("\n")


def import_keys(proto, username):
	"""
	Import keys from service at 'proto' for 'username', appending to output file
	"""
	# Map out which keys we already have, so we don't keep appending the same ones
	local_keys = key_list(read_keyfile())
	# Protocol handler should output SSH keys, one per line
	result = []
	keyfile_lines = []
	comment_string = "# ssh-import-id %s:%s" % (proto, username)
	for line in fetch_keys(proto, username):
		# Validate/clean-up key text
		line = line.decode('utf-8').strip()
		fields = line.split()
		fields.append(comment_string)
		ssh_fp = key_fingerprint(fields)
		if ssh_fp:
			if fp_tuple(ssh_fp) in local_keys:
				logging.info("Already authorized %s" % (ssh_fp[:3] + ssh_fp[-1:]))
				result.append(fields)
			else:
				keyfile_lines.append(" ".join(fields))
				result.append(fields)
				logging.info("Authorized key %s" % (ssh_fp[:3] + ssh_fp[-1:]))
	write_keyfile(keyfile_lines, "a+")
	return result


def remove_keys(proto, username):
	"""
	Remove keys from the output file, if they were inserted by this tool
	"""
	# Only remove keys labeled with our comment string
	comment_string = "# ssh-import-id %s:%s\n" % (proto, username)
	update_lines = []
	removed = []
	for line in read_keyfile():
		if line.endswith(comment_string):
			ssh_fp = key_fingerprint(line.split())
			logging.info("Removed labeled key %s" % (ssh_fp[:3] + ssh_fp[-1:]))
			removed.append(line)
		else:
			update_lines.append(line)
	write_keyfile(update_lines, "w")
	return removed


if __name__ == '__main__':
	errors = []
	try:
		os.umask(0o177)
		parser.options = parser.parse_args()
		keys = []
		for userid in parser.options.userids:
			user_pieces = userid.split(':')
			if len(user_pieces) == 2:
				proto, username = user_pieces
			elif len(user_pieces) == 1:
				proto, username = DEFAULT_PROTO, userid
			else:
				die("Invalid user ID: [%s]" % (userid))
			if parser.options.remove:
				k = remove_keys(proto, username)
				keys.extend(k)
				action = "Removed"
			else:
				k = import_keys(proto, username)
				keys.extend(k)
				action = "Authorized"
			if len(k) == 0:
				errors.append(userid)
		logging.info("[%d] SSH keys [%s]" % (len(keys), action))
	except (Exception,):
		e = sys.exc_info()[1]
		die("%s" % (str(e)))
	cleanup()
	if len(errors) > 0:
		die("No matching keys found for [%s]" % ','.join(errors))
	os._exit(0)