expiring_token_generator.py

from datetime import datetime, timedelta

import cryptography
from cryptography.fernet import Fernet

class ExpiringTokenGenerator:
  FERNET_KEY = 'H-gvBa31So7ZWRlIleY7q5xYPIytGnRHRcBpRbASyao='
  fernet = Fernet(FERNET_KEY)

  DATE_FORMAT = '%Y-%m-%d %H-%M-%S'
  EXPIRATION_DAYS = 3

  def _get_time(self):
    """Returns a string with the current UTC time"""
    return datetime.utcnow().strftime(self.DATE_FORMAT)

  def _parse_time(self, d):
    """Parses a string produced by _get_time and returns a datetime object"""
    return datetime.strptime(d, self.DATE_FORMAT)

  def generate_token(self, text):
    """Generates an encrypted token"""
    full_text = text + '|' + self._get_time()
    token = self.fernet.encrypt(bytes(full_text))

    return token

  def get_token_value(self, token):
    """Gets a value from an encrypted token.

    Returns None if the token is invalid or has expired.
    """
    try:
      value = self.fernet.decrypt(bytes(token))
      separator_pos = value.rfind('|')

      text = value[: separator_pos]
      token_time = self._parse_time(value[separator_pos + 1: ])
      
      if token_time + timedelta(self.EXPIRATION_DAYS) < datetime.utcnow():
        return None

    except cryptography.fernet.InvalidToken:
      return None

    return text 

  def is_valid_token(self, token):
    return self.get_token_value(token) != None