Decode a jwt from stdin, without using jwt.io or external libraries

jwt-decode.py

#!/usr/bin/env python3

import base64
import json
import fileinput

for jwt in fileinput.input():
    parts = jwt.split(".")

    # '==' is padding
    parts = dict(
        header = parts[0] + '==',
        data = parts[1] + '==',
        signature = parts[2] + '=='
    )

    decoded_parts = dict()

    for name, part in parts.items():
        decoded = base64.urlsafe_b64decode(part.encode('utf8'))
        try:
            # parse the json string
            decoded_parts[name] = json.loads(decoded.decode('utf8'))
        except UnicodeDecodeError as e:
            # signatures are binary, so don't try to unicode-decode them
            decoded_parts[name] = part

    print(json.dumps(decoded_parts, indent=4))