Amazon Simple Notification Service or SNS is a messaging service which be used to send notifications by SMS, Email, Push notification or to a URL endpoint.

For a quick on setting up Amazon SNS see this article Amazon SNS setup for HTTPS and Email

Code for auto confirmation of subscriptions

<?php
$json_write_to_text = file_get_contents("php://input"); //read the raw data 
$json_write_to_text = json_decode($json_write_to_text, TRUE, 512, JSON_OBJECT_AS_ARRAY);

if($json_write_to_text['Type'] == SubscriptionConfirmation)
{
 $curl = curl_init();

 curl_setopt_array($curl, array(
  CURLOPT_URL => $json_write_to_text['SubscribeURL'],
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_CUSTOMREQUEST => "GET",
  CURLOPT_HTTPHEADER => $header,
 ));

 $response = curl_exec($curl);
 $err = curl_error($curl);

 curl_close($curl);
}

file_put_contents("response.txt",print_r($json_write_to_text,true)); // this is just for dumping the raw data and can be omitted 
?>

Login to AWS Console

Goto Simple Notification Service

Create a Topic

Add a Subscription – the easy and safe way to do this is by clicking the ARN of the Topic (in the topic listing page ) and going to the Topic details page.

Choose your subscription protocol (in simpler words in which way you want the notifications to be delivered)

Amazon SNS will do a verification. The method depends on the protocol chosen. For example for emails it will send an email with a verification link, for HTTP or HTTPS it will call the endpoint with some data like below. On opening or hitting the SubscribeURL the verification will be complete.

Array
(
[Type] => SubscriptionConfirmation
[MessageId] => eeexxxea-xxxx-xxxx-xxxx-c15xxxx81361
[Token] => 2336412f3xxxxxxxxxxxxxxxxxxxxxxxxee34aadbb4eb9c926c288f8ca1xxxxxxxxxxxxcbe27c6835edd47bd28d0cf1d0cb9b4xxxxxxxx1003b95c6bc1231db657b1bb465a7d98c73a8d79faddb473a1a109c45654a1db1f11xxxxxxxxxxxxxxxxxxxf74dae61acfbe2f508901390b2cd6
[TopicArn] => arn:aws:sns:us-east-x:0xxxxxxxxxx9:xxx-bounce
[Message] => You have chosen to subscribe to the topic arn:aws:sns:us-east-x:0xxxxxxxxxx9:xxx-bounce.
To confirm the subscription, visit the SubscribeURL included in this message.
[SubscribeURL] => https://sns.us-east-1.amazonaws.com/?Action=ConfirmSubscription&TopicArn=arn:aws:sns:us-east-x:0xxxxxxxxxx9:xxx-bounce&Token=2336412f3xxxxxxxxxxxxxxxxxxxxxxxxee34aadbb4eb9c926c288f8ca1xxxxxxxxxxxxcbe27c6835edd47bd28d0cf1d0cb9b4xxxxxxxx1003b95c6bc1231db657b1bb465a7d98c73a8d79faddb473a1a109c45654a1db1f11xxxxxxxxxxxxxxxxxxxf74dae61acfbe2f508901390b2cd6
[Timestamp] => 2019-01-09T14:53:31.247Z
[SignatureVersion] => 1
[Signature] => euyT80G1NujWgQMWfltxxxxxxxxxxxxxxxiDqeicbE1FH5dwdBnAA7UY84zHf0fsJCd/xxxxxxxxxxxxxxxxxxxxxxxxx/rxx/t/wKxxxxxx/LKg2QwcjGPdnIh4xp6rNA4PKihOjMiPfTZYH4kQV+h+4zqFsQT1UL+ixlM+xBZqZY3zUV1lrHKz+SfIkPJxxxxxxxxxxIB2FN0O2leokHJYRlUqxxxxxxkMzlbsMg4ChDW8+hcJ14hNEz5kpM5T0Fqljt2CmqkF1BQ68ViTgFV7yYpcSTbejo0DuZAUxxxxxxxxxx5y340TcfTWWq+3hKSTtB9aTclgDchvLDYKNqg==
[SigningCertURL] => https://sns.us-east-x.amazonaws.com/SimpleNotificationService-ac56xxxxxxxxxxxxxxxxxxxx8aa1d9b.pem
)

Once the verification is complete the Subscription ID will show an ARN. See The Topic Details picture.

Sample PHP code for auto-verification of SNS Subscriptions for HTTP/HTTPS protocols PHP code for Amazon SNS Auto Subscription Confirmation (HTTPS)