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How to use the pre-request script?

For Postman, simply add the given code snippet into postman pre-request script tab. Postman Pre-Request Script: 
var epoch = (new Date).getTime();
var epochSecs = Math.floor( epoch / 1000 );
pm.collectionVariables.set("epoch", epochSecs);
var data = epochSecs.toString() + environment["api_key"];
var hmacDigest = CryptoJS.enc.Hex.stringify(CryptoJS.HmacSHA512(data, environment["api_secret"]));
pm.collectionVariables.set("checksum", hmacDigest);

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Why pre-request script is needed?

We use checksum calculation in pre-request script, It is required to authenticate the CHIP Send API. It acts as an extra layer of protection to mitigate data tampering and prevent replay attacks.

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Pre-request script in other languages

Example Ruby code: 
epoch = Time.current.to_i
application = Application.find_by(slug: "aaa")
OpenSSL::HMAC.hexdigest OpenSSL::Digest.new('sha512'), application.api_secret, "#{epoch}#{application.api_key}"
Example PHP code: 
<?php

$str = '1689826456e0645c9e-fcf2-4f29-a327-202f7ed3d969';
$hmac = hash_hmac( 'sha512', $str, 'a118729e-4243-4145-83b3-0b8cb213fe8e' );

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FAQ

Frequently asked questions regarding pre-request script.
  1. Where can I get api_key and api_secret?
    For api_key, you can obtain it from the CHIP Control Applications
    For api_secret, you need to request from CHIP sales team
  2. What hashing algorithm is used for pre-request script?
    The hashing algorithm used is SHA-512