215 lines
8.5 KiB
Python
215 lines
8.5 KiB
Python
"""The tokens of the router's web service, for the web service and vpn-router-token.
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Tokens are HS256 JWTs signed with WEB_KEY, a key the web service makes on its first run on the
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router and that never leaves it. /auth issues an access token naming the user in sub, valid ACCESS_SECONDS, and
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a refresh token valid REFRESH_SECONDS; vpn-router-token issues tokens with the admin claim and
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any lifetime. A token without the admin claim must expire within MAX_LIFETIME seconds.
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psycopg is imported by driver() when the database is used, not when the module is loaded, so the
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module loads while libpq cannot be found yet. A driver that cannot be imported and every
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failure of the database raise DatabaseError, the only database exception callers see.
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Refresh tokens are random strings kept in PostgreSQL as their SHA-256, in the database of
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web.database, by default the vpn-router database on this host that provision() creates on the
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web service's first run, with the password in DATABASE_SECRET. A refresh token is used once: refreshing replaces it.
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"""
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import base64
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import contextlib
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import hashlib
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import hmac
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import json
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import pathlib
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import secrets
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import subprocess
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import time
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WEB_KEY = pathlib.Path('/etc/vpn-router/web.key')
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DATABASE_SECRET = pathlib.Path('/etc/vpn-router/database.secret')
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#: The role and the database provision() creates when web.database is not set.
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DATABASE = 'vpn-router'
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#: Seconds an access token of /auth and a refresh token are valid.
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ACCESS_SECONDS = 300
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REFRESH_SECONDS = 8 * 3600
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#: The longest a token without the admin claim may be valid, from now, in seconds.
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MAX_LIFETIME = 600
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#: Seconds of clock difference accepted between a token and this router.
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LEEWAY = 60
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SCHEMA = 'CREATE TABLE IF NOT EXISTS refresh_tokens (hash text PRIMARY KEY, name text NOT NULL, expires timestamptz NOT NULL)'
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class DatabaseError(Exception):
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"""The PostgreSQL driver cannot be loaded, or the database of the refresh tokens failed."""
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def key():
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"""The signing key, or '' while the web service has not made it."""
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try:
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return WEB_KEY.read_text(encoding='utf-8').strip()
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except OSError:
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return ''
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def ensure_key():
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"""Make the signing key when it is missing."""
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if not key():
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WEB_KEY.parent.mkdir(parents=True, exist_ok=True)
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WEB_KEY.touch(mode=0o600)
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WEB_KEY.chmod(0o600)
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WEB_KEY.write_text(secrets.token_urlsafe(36) + '\n', encoding='utf-8')
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def b64encode(data):
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return base64.urlsafe_b64encode(data).rstrip(b'=').decode()
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def b64decode(part):
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return base64.urlsafe_b64decode(part + '=' * (-len(part) % 4))
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def sign(claims, secret):
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head = b64encode(json.dumps({'alg': 'HS256', 'typ': 'JWT'}).encode())
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body = b64encode(json.dumps(claims).encode())
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signature = hmac.new(secret.encode(), f'{head}.{body}'.encode(), hashlib.sha256).digest()
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return f'{head}.{body}.{b64encode(signature)}'
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def verify(token, secret):
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"""The claims of a token signed with HS256 by the secret, or None when it is not acceptable.
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Only HS256 is accepted, so a token cannot choose a weaker algorithm. The token must expire
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(exp); without the admin claim not later than MAX_LIFETIME seconds from now, so that a stolen
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token is of little use. LEEWAY seconds of clock difference are allowed.
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"""
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try:
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header, payload, signature = token.split('.')
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if json.loads(b64decode(header)).get('alg') != 'HS256':
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return None
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expected = hmac.new(secret.encode(), f'{header}.{payload}'.encode(), hashlib.sha256).digest()
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if not hmac.compare_digest(expected, b64decode(signature)):
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return None
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claims = json.loads(b64decode(payload))
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now = time.time()
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expires = claims['exp']
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if isinstance(expires, bool) or not isinstance(expires, (int, float)) or expires < now - LEEWAY:
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return None
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if claims.get('admin') is not True and expires > now + MAX_LIFETIME + LEEWAY:
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return None
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not_before = claims.get('nbf')
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if not_before is not None and (isinstance(not_before, bool) or not isinstance(not_before, (int, float)) or not_before > now + LEEWAY):
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return None
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except (ValueError, KeyError, TypeError, AttributeError):
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return None
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return claims
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def admin_token(seconds):
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"""A token with the admin claim, valid for the seconds given."""
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secret = key()
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if not secret:
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raise OSError(f'{WEB_KEY} does not exist; vpn-router-web makes it when it starts')
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now = int(time.time())
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return {'token': sign({'admin': True, 'iat': now, 'exp': now + seconds}, secret), 'expires': now + seconds}
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def driver():
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"""The psycopg module; DatabaseError while libpq cannot be found."""
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try:
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import psycopg
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except ImportError as exc:
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raise DatabaseError(f'the PostgreSQL driver cannot be loaded: {exc}') from exc
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return psycopg
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def connection_string(cfg):
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"""web.database, or the database provision() creates; its password, of URL-safe characters, is written unquoted."""
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configured = cfg['web']['database'].strip()
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if configured:
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return configured
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password = DATABASE_SECRET.read_text(encoding='utf-8').strip()
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return f'host=localhost dbname={DATABASE} user={DATABASE} password={password}'
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@contextlib.contextmanager
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def database(cfg):
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"""A connection to the database of the refresh tokens, with their table, closed at the end; DatabaseError on any failure."""
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psycopg = driver()
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try:
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with psycopg.connect(connection_string(cfg), autocommit=True) as connection:
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connection.execute(SCHEMA)
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yield connection
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except psycopg.Error as exc:
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raise DatabaseError(f'the token database failed: {exc}') from exc
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def digest(token):
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return hashlib.sha256(token.encode()).hexdigest()
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def issue(cfg, name):
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"""An access token and a refresh token for the user, as /auth answers them."""
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secret = key()
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now = int(time.time())
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refresh = secrets.token_urlsafe(32)
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with database(cfg) as connection:
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connection.execute('DELETE FROM refresh_tokens WHERE expires < now()')
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connection.execute("INSERT INTO refresh_tokens VALUES (%s, %s, now() + make_interval(secs => %s))",
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(digest(refresh), name, REFRESH_SECONDS))
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return {
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'access_token': sign({'sub': name, 'iat': now, 'exp': now + ACCESS_SECONDS}, secret),
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'token_type': 'Bearer',
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'expires_in': ACCESS_SECONDS,
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'refresh_token': refresh,
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'refresh_expires_in': REFRESH_SECONDS,
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}
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def take(cfg, token):
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"""Remove an unexpired refresh token and return the user it was issued to, or None."""
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if not isinstance(token, str) or not token:
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return None
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with database(cfg) as connection:
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row = connection.execute('DELETE FROM refresh_tokens WHERE hash = %s RETURNING name, expires > now()',
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(digest(token),)).fetchone()
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return row[0] if row and row[1] else None
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def revoke(cfg, name):
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"""Remove all refresh tokens of the user."""
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with database(cfg) as connection:
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connection.execute('DELETE FROM refresh_tokens WHERE name = %s', (name,))
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def psql(sql, name):
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"""The output of an SQL statement, read from standard input, run by psql as postgres with name as the variable v1."""
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args = ['runuser', '-u', 'postgres', '--', 'psql', '-X', '-q', '-t', '-A', '-v', 'ON_ERROR_STOP=1', '-v', f'v1={name}']
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result = subprocess.run(args, input=sql, capture_output=True, text=True)
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if result.returncode != 0:
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raise OSError(f'psql failed: {result.stderr.strip()}')
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return result.stdout.strip()
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def provision(cfg):
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"""Create the role, its password file and the database when web.database is not set and they are missing.
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The password, of URL-safe characters, reaches psql on standard input, not on its command line.
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"""
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if cfg['web']['database'].strip():
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return
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if not psql("SELECT 1 FROM pg_roles WHERE rolname = :'v1'", DATABASE):
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DATABASE_SECRET.unlink(missing_ok=True)
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psql("CREATE ROLE :\"v1\" LOGIN", DATABASE)
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if not DATABASE_SECRET.is_file():
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password = secrets.token_urlsafe(32)
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psql(f"ALTER ROLE :\"v1\" PASSWORD '{password}'", DATABASE)
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DATABASE_SECRET.touch(mode=0o600)
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DATABASE_SECRET.chmod(0o600)
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DATABASE_SECRET.write_text(password + '\n', encoding='utf-8')
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if not psql("SELECT 1 FROM pg_database WHERE datname = :'v1'", DATABASE):
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psql("CREATE DATABASE :\"v1\" OWNER :\"v1\"", DATABASE)
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