add token support to script to support ssh forced commands with tokens

README.md

@@ -1,13 +1,14 @@
 # PowerDNS - Letsencrypt
 
-This role extends the PowerDNS role with another backend to handle Letsencrypt challanges.
+This role extends the PowerDNS role with another backend to handle Letsencrypt challenges.
 
 ## operation
 
 We register a [PowerDNS pipe backend](https://doc.powerdns.com/authoritative/backends/pipe.html) and deploy a python script to serve it.
 The script is stored at `/usr/local/bin/pdns.py`. This script processes queries matching the regex `^_acme-challenge\\.`.
-It can also be called directly with `pdns.py <dns entry> <value>` to add challanges, for example `pdns.py "_acme-challenge.example.com" "R8aa0mt6cnCVLF6RHsSNxmDBzJffNCK6"`
-Challanges older than two days are removed when a new entry is added.
+It can also be called directly with `pdns.py add_challenge <dns entry> <value>` to add challenges, for example `pdns.py add_challenge "_acme-challenge.example.com" "R8aa0mt6cnCVLF6RHsSNxmDBzJffNCK6"`
+Challenges older than two days are removed when a new entry is added.
+This can be automated using tokens (see `pdns.py --help`) and ssh forced commands.
 
 ## parameters
 

tasks/main.yml

@@ -1,7 +1,14 @@
-- name: install powerdns backends
+- name: install powerdns backends and dependencies
   apt:
     pkg:
     - "pdns-backend-pipe"
+    - "python3-click"
+
+- name: create letsencrypt user
+  user:
+    name: letsencrypt
+    password: '*'
+    system: True
 
 - name: create folders
   file:
@@ -11,7 +18,14 @@
     group: "{{ item.group|d('pdns') }}"
     mode: "{{ item.mode|d('0755') }}"
   with_items:
-  - { "path": "/var/lib/powerdns/letsencrypt/" }
+  - { "path": "/var/lib/powerdns/letsencrypt/", "owner": "letsencrypt" }
+
+- name: ensure database permissions
+  file:
+    path: "{{ powerdns.letsencrypthandler.dbpath }}"
+    owner: letsencrypt
+    group: pdns
+    mode: 0644
 
 - name: copy powerdns letsencrypt handler
   template:

templates/pdns-letsencrypt.py.j2

@@ -1,8 +1,10 @@
 #!/usr/bin/env python3
 import sys
-from sys import stdin, stdout
+from sys import stdin, stdout, stderr
+import os
 import socket
 import sqlite3
+import click
 
 def setupdb():
 	conn = sqlite3.connect('{{ powerdns.letsencrypthandler.dbpath }}', isolation_level=None)
@@ -13,24 +15,58 @@ def setupdb():
 			timestamp	DEFAULT	(strftime('%s','now'))
 		)
 	""")
+	conn.executescript("""
+		CREATE TABLE IF NOT EXISTS tokens (
+			token	TEXT	NOT NULL,
+			record	TEXT	NOT NULL,
+			last_used	DEFAULT	(strftime('%s','now')),
+			added	DEFAULT	(strftime('%s','now')),
+			UNIQUE(token, record)
+		)
+	""")
 	conn.commit()
 	return conn
 
-def get_challenge(db, path):
+def cleanup_db(db):
 	c = db.cursor()
-	c.execute('SELECT value FROM challenges WHERE q = ?', (path,))
+	c.execute("DELETE FROM challenges WHERE timestamp < strftime('%s', datetime('now','-2 day'))")
+	db.commit()
+
+def get_challenge(db, record):
+	c = db.cursor()
+	c.execute('SELECT value FROM challenges WHERE q = ?', [record])
 	result = c.fetchall()
 	if result:
 		return result
 	else:
-		return ['NO DATA - ' + socket.gethostname()]
+		return [['NO DATA -' + socket.gethostname()]]
 
-def add_challenge(db, path, value):
+def add_challenge(db, record, value):
 	c = db.cursor()
-	c.execute('INSERT INTO challenges (q, value) VALUES(?, ?)', (path,value,))
-	c.execute("DELETE FROM challenges WHERE timestamp < strftime('%s', datetime('now','-2 day'))")
+	c.execute('INSERT INTO challenges (q, value) VALUES(?, ?)', [record, value])
 	db.commit()
 
+def add_token(db, token, record):
+	c = db.cursor()
+	c.execute('INSERT OR IGNORE INTO tokens (token, record, last_used) VALUES(?, ?, NULL)', [token, record])
+	db.commit()
+
+def token_has_access(db, token, record):
+	c = db.cursor()
+	c.execute('SELECT * FROM tokens WHERE token = ? AND record = ?', [token, record])
+	result = c.fetchall()
+	if result:
+		c.execute("UPDATE tokens SET last_used = strftime('%s','now') WHERE token = ? AND record = ?", [token, record])
+		db.commit()
+		return True
+	else:
+		return False
+
+@click.group()
+def cli():
+	pass
+
+@cli.command(name="pdns_backend")
 def main_query():
 	db = setupdb()
 	data = stdin.readline()
@@ -38,6 +74,8 @@ def main_query():
 	stdout.flush()
 	while True:
 		data = stdin.readline().strip()
+		if not data:
+			continue
 		kind, qname, qclass, qtype, id, ip = data.split("\t")
 		if qtype == "SOA":
 			stdout.write("DATA\t" + qname + "\t" + qclass + "\t" + qtype + "\t300\t" + id + "\t")
@@ -49,15 +87,50 @@ def main_query():
 		stdout.write("END\n")
 		stdout.flush()
 
-def main_add_challenge():
+@cli.command(name="add_challenge")
+@click.argument('record')
+@click.argument('challenge')
+def main_add_challenge(record, challenge):
 	db = setupdb()
-	add_challenge(db ,sys.argv[1], sys.argv[2])
+	add_challenge(db, record, challenge)
+	cleanup_db(db)
 
-def main():
-	if len(sys.argv) == 3:
-		main_add_challenge()
+@cli.command(name="add_challenge_with_token")
+@click.argument('token')
+@click.argument('record')
+@click.argument('challenge')
+def main_add_challenge_with_token(token, record, challenge):
+	db = setupdb()
+	if token_has_access(db, token, record):
+		add_challenge(db, record, challenge)
+		cleanup_db(db)
+		exit(0)
 	else:
-		main_query()
+		cleanup_db(db)
+		print("Token does not have access to this record")
+		exit(1)
+
+@cli.command(name="add_challenge_with_token_ssh")
+@click.pass_context
+def main_add_challenge_with_token_ssh(ctx):
+	# ssh passes the SSH_ORIGINAL_COMMAND environment variable if you use a forced command
+	# using this we can support auto renew hooks like this:
+	# ssh letsencrypt@server <token> <record> <challenge>
+	cmd = os.environ.get('SSH_ORIGINAL_COMMAND')
+	if not cmd:
+		exit(2)
+	cmd = cmd.strip().split(' ')
+	if len(cmd) != 3:
+		exit(3)
+	ctx.invoke(main_add_challenge_with_token, token=cmd[0], record=cmd[1], challenge= cmd[2])
+
+@cli.command(name="add_token")
+@click.argument('token')
+@click.argument('record')
+def main_add_token(token, record):
+	db = setupdb()
+	add_token(db, token, record)
+	cleanup_db(db)
 
 if __name__ == '__main__':
-	main()
+	cli()

vars/main.yml

@@ -3,5 +3,5 @@ powerdns:
     launch:
       "pipe:letsencrypt": {}
     "pipe-letsencrypt-regex": "^_acme-challenge\\."
-    "pipe-letsencrypt-command": "/usr/local/bin/pdns.py"
+    "pipe-letsencrypt-command": "/usr/local/bin/pdns.py pdns_backend"
     "pipe-letsencrypt-abi-version": "1"