parse or verify a Ziti enrollment token as JWT

ziti-jwt.py

#!/usr/bin/env python

# This script parses and attempts to verify the signature of a Ziti JWT token and prints the header, payload, and
# analysis of the token.

import argparse
import json
import logging
import os
import ssl
import socket
from datetime import datetime
from urllib.parse import urlparse

import chardet
import humanize
import jwt
from OpenSSL import crypto


def detect_encoding(file_path):
    with open(file_path, 'rb') as file:
        data = file.read()
    return chardet.detect(data)['encoding']


def get_file_content_or_string(s):
    if os.path.isfile(s):
        with open(s, 'rb') as file:
            return file.read().decode(detect_encoding(s), 'strict').strip()
    else:
        return s


def parse_verify_jwt(token, key: str = None):
    claimset = jwt.decode(
        jwt=token,
        key=key,
        algorithms=["ES256", "RS256"],
        options={
            "verify_signature": True if key else False,
            "verify_aud": False,
            "verify_exp": False,
        }
    )
    return claimset


def fetch_issuer_pubkey(iss: str):
    url = urlparse(iss)
    # Get the server's certificate
    cert = ssl.get_server_certificate((url.hostname, url.port or 443), timeout=3)
    # Get the public key from the certificate
    x509 = crypto.load_certificate(crypto.FILETYPE_PEM, cert)
    pubkey = crypto.dump_publickey(crypto.FILETYPE_PEM, x509.get_pubkey())
    return pubkey


# Create the parser
parser = argparse.ArgumentParser(description="Process some integers.")

# Add the positional arguments
parser.add_argument('token', type=str, help='The token to verify (required) as a string or file path')
parser.add_argument('pubkey', type=str, nargs='?', default=None, help='The client API\'s pubkey (optional) as a string or file path')

# Add the --verbose option
parser.add_argument('-v', '--verbose', action='store_true', help='Set log level to DEBUG')

# Parse the arguments
args = parser.parse_args()

# Create a custom logger
logger = logging.getLogger(__name__)

# Create handlers
c_handler = logging.StreamHandler()
c_handler.setLevel(logging.INFO)

# Create formatters and add it to handlers
c_format = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
c_handler.setFormatter(c_format)

# Add handlers to the logger
logger.addHandler(c_handler)

# Set up logging
logging.basicConfig(level=logging.DEBUG if args.verbose else logging.INFO)

token = get_file_content_or_string(args.token)

if args.pubkey:
    pubkey = get_file_content_or_string(args.pubkey)
else:
    claimset = parse_verify_jwt(token)
    try:
        pubkey = fetch_issuer_pubkey(claimset["iss"])
    except (TimeoutError, socket.gaierror) as e:
        logger.debug(f"failed to fetch issuer pubkey: {e}")
        pubkey = None

if pubkey:
    logger.debug(f"verifying '{token}' with pubkey '{pubkey}'")
else:
    logger.debug(f"parsing '{token}' without a pubkey for signature verification")

header = jwt.get_unverified_header(token)

try:
    claimset = parse_verify_jwt(token, pubkey)
    if pubkey:
        signature_valid = True
    else:
        signature_valid = False
except jwt.exceptions.InvalidSignatureError:
    signature_valid = False

if 'em' in claimset:
    if claimset['em'] == 'ott':
        enrollment_method = 'one-time token for an identity from the built-in edge signer CA'
    elif claimset['em'] == 'ottca':
        enrollment_method = 'one-time token for a an identity from a trusted external CA'
    elif claimset['em'] == 'ca':
        enrollment_method = 'reusable token for auto-creating an identity from a trusted external CA'
    elif claimset['em'] == 'erott':
        enrollment_method = 'one-time token for a router'
    else:
        enrollment_method = 'unknown'

analysis = {
    "signature_valid": signature_valid,
    "enrollment_method": enrollment_method
}

if 'exp' in claimset:
    expiration_time = datetime.fromtimestamp(claimset['exp'])
    expires_in = expiration_time - datetime.now()
    if expires_in.total_seconds() > 0:
        analysis['expiration'] = (
            f"valid until {expiration_time.isoformat()} "
            f"({humanize.naturaldelta(expires_in)})"
        )
    else:
        expires_ago = -expires_in
        analysis['expiration'] = (
            f"expired since {expiration_time.isoformat()} "
            f"({humanize.naturaldelta(expires_ago)})"
        )

print(
    json.dumps({
        "header": header,
        "payload": claimset,
        "analysis": analysis
    }, indent=4)
)