Generating HMAC sha256 from JSON request payload in jmeter

Question

I am setting up a test plan in jmeter in which a Sampler is an HTTP POST request. I have to send a JSON payload in the request body. Now, for authentication purposes, I have to create an HMAC sha256 code using a secret which will be passed in the header of the request. How can I create the HMAC in the preProcessor script?

Rob Evans Rob Evans · Accepted Answer · 2020-08-25T22:09:06

I've done something similar before with the following:

    public static Mac SHARED_MAC;

    static {
        try {
            SHARED_MAC = Mac.getInstance("HmacSHA256");
        } catch (NoSuchAlgorithmException nsaEx) {
            nsaEx.printStackTrace();
        }
    }

private String secretKey; // set this in a constructor or pass to the method below

public String generateSignature(String requestPath, String method, String body, String timestamp) {
        try {
            String prehash = timestamp + method.toUpperCase() + requestPath + body;
            byte[] secretDecoded = Base64.getDecoder().decode(secretKey);
            SecretKeySpec keyspec = new SecretKeySpec(secretDecoded,  SHARED_MAC.getAlgorithm());
            Mac sha256 = (Mac) SHARED_MAC.clone();
            sha256.init(keyspec);
            return Base64.getEncoder().encodeToString(sha256.doFinal(prehash.getBytes()));
        } catch (CloneNotSupportedException | InvalidKeyException e) {
            e.printStackTrace();
            throw new RuntimeErrorException(new Error("failed")); // fatal error - exits program
        }
    }

HTH in some way

Generating HMAC sha256 from JSON request payload in jmeter

1 Answers