env.message.senderparameter provided during contract execution is legitimate, so we will confirm that
env.message.sender == predefined_address. If this condition is met we can provide admin functionality. If the
env.message.senderparameter can be tampered with — we effectively can't rely on it and cannot implement the admin interface.
callback_signaturebased on parameters it sends, passes it on to the next contract
callback_signaturebased on the parameter it got.