Read verification code automatically and access for Login in App in iOS

I am creating one App and it has verification phone number required functionality which allow user to enter into App. We send sms to the Users through the gateway and we need to read verification code directly from the SMS without typing code into App. But don't know how to read verification code automatic from the SMS and access in my App.I have gone thorugh the searches for this but could not find any path to move ahead. Is it allow in iOS and if Yes, can anyone tell me what to do to achieve it. Thanks.