Python implement of https://gist.github.com/wildjcrt/6359713fa770d277927051fdeb30ebbf?permalink_comment_id=4157641#gistcomment-4157641

ruby_on_rails_v7_auth_secure_session_cookie_decrypt.py

import hashlib
import base64
import json
import urllib.parse
from Crypto.Cipher import AES


# Decrypt Discourse auth sercure session cookie
# Refer: https://gist.github.com/wildjcrt/6359713fa770d277927051fdeb30ebbf?permalink_comment_id=4157641
def decrypt_secure_session_cookie(cookie, secret_key_base):
    # cookie: value of '_t' cookie
    # secret_key_base: Rails.application.config.secret_key_base
        cookie = urllib.parse.unquote(cookie)
        data, iv, auth_tag = cookie.split('--')
        data = data.encode('utf8')
        iv = iv.encode('utf8')
        auth_tag = auth_tag.encode('utf8')

        data = base64.b64decode(data + b'=' * (-len(data) % 4))
        iv = base64.b64decode(iv + b'=' * (-len(iv) % 4))
        auth_tag = base64.b64decode(auth_tag + b'=' * (-len(auth_tag) % 4))
        
        # salt = Rails.application.config.action_dispatch.authenticated_encrypted_cookie_salt
        secret = hashlib.pbkdf2_hmac('sha1', secret_key_base.encode('utf8'), b'authenticated encrypted cookie', 1000, dklen=32)
        cipher = AES.new(secret, AES.MODE_GCM, iv)
        cookie_payload = cipher.decrypt_and_verify(data, auth_tag).decode('utf8')
        cookie_payload = json.loads(cookie_payload)
        decoded_stored_value = base64.b64decode(cookie_payload["_rails"]["message"])
        return json.loads(decoded_stored_value)