new_contents: from django.conf import settings
  from django.core.signing import TimestampSigner
  from django.core.signing import BadSignature, SignatureExpired
  
  
  def generate_key(user):
      signer = TimestampSigner(settings.SECRET_KEY)
      return signer.sign(str(user.id))
  
  
  def validate_key(key, user):
      signer = TimestampSigner(settings.SECRET_KEY)
      try:
          value = signer.unsign(key, max_age=settings.EMAIL_LINK_EXPIRY_DAYS)
          return str(user.id) == value
      except (BadSignature, SignatureExpired):
          return False
  
subject: Add `activation_service`