webhook validation mailpace laravel/php

webhook.php

<?php
// Retrieve the signature from the request headers and decode it from base64
$signature_base64 = $request->header('X-MailPace-Signature');
$signature = base64_decode($signature_base64);
if ($signature === false) {
    // Invalid signature encoding
    abort(400, 'Invalid signature encoding');
}

// Decode your public key from base64
$verify_key_base64 = 'Your Public Key from app.mailpace.com here';
$verify_key = base64_decode($verify_key_base64);
if ($verify_key === false) {
    // Invalid public key encoding
    abort(500, 'Invalid public key encoding');
}

// Retrieve the raw body of the request
$message = $request->getContent();

// Verify the signature
$isValid = sodium_crypto_sign_verify_detached($signature, $message, $verify_key);

if ($isValid) {
    // Verification passed
    return response('Verification passed', 200);
} else {
    // Verification failed
    abort(400, 'Invalid signature');
}

I've tested this with a raw body string pulled directly from the HTTP request, and it verifies successfully, for example:

$message = '{"event":"email.queued","payload":{"status":"queued","id":11614086,"domain_id":11,"created_at":"2024-09-18T16:30:09.314Z","updated_at":"2024-09-18T16:30:09.314Z","from":"[email protected]","to":"[email protected]","htmlbody":null,"textbody":"test\n","cc":null,"bcc":"","subject":"Test for gmail - gmail","replyto":null,"message_id":"\[email protected]\u003e","list_unsubscribe":null}}';

Which suggests to me that something is being changed from the raw request body here in laravel. Perhaps an encoding issue or similar. Here is how we create the webhook signature in Ruby - the $message needs to match the body exactly for the verification to succeed.

https://blog.mailpace.com/blog/how-to-verify-webhooks-with-elliptic-key-cryptography-ed25519/

Ok will test it out thanks for now!

@paul-oms seems this is not working (the signature from the header) with strict set to true in base64_decode (https://www.php.net/base64_decode).

$message = '';

$signature = base64_decode("sHnRyHCzMpHhMrWT5\/GynEWzryRQG7FvWcCvvKHjDWV6r+\/X+OzG4YMpua78I7CYh+qC3hK9xXZlYHePZHopCg==", true);

$verify_key = base64_decode('private-key', true);

$isValid = sodium_crypto_sign_verify_detached($signature, $message, $verify_key);

this gives me an error:

sodium_crypto_sign_verify_detached(): Argument #1 ($signature) must be SODIUM_CRYPTO_SIGN_BYTES bytes long

EDIT:

seems not to happen on all signature headers... strange

EDIT2:
I removed the strict parameter from base64_decode, and it seems to work now

strict decode should work on the signature. However I think I've found the root cause. It looks like Laravel (or something in the stack) automatically converts Unicode escape sequences when getContent() is called. So e.g. "message_id":"\[email protected]\u003e" is converted to "message_id":"<[email protected]>"

This won't match the original email we sign on our end, therefore preventing the signatures from matching - i'm checking for a way to get the original request without this

Looks like this should work:

$message = json_encode($response->getOriginalContent(), JSON_HEX_TAG);

Try that and let me know if you still face problems