We’re implementing a secure webhook consumer in our Kotlin backend to handle routing.queue.member events from Genesys Cloud. The goal is to prevent replay attacks by verifying the X-Genesys-Signature header and ensuring the request timestamp hasn’t drifted too far from our server time.
I’ve been following the documentation for Verifying Webhook Signatures, but the validation logic keeps failing with a SignatureVerificationException. The issue seems to be with how I’m handling the timestamp validation window. Genesys sends the signature as t=1678886400;v0=abc123.... I’m parsing the t value and comparing it to System.currentTimeMillis() / 1000, allowing a 30-second skew.
Here’s the core verification snippet in Kotlin:
fun verifySignature(payload: String, signatureHeader: String, secret: String): Boolean {
val parts = signatureHeader.split(";")
val timestamp = parts[0].split("=")[1].toLong()
val currentTs = System.currentTimeMillis() / 1000
if ((currentTs - timestamp).abs() > 30) {
throw SignatureVerificationException("Timestamp drift too large: ${currentTs - timestamp}")
}
val expectedSig = hmacSha256(secret, "$timestamp.$payload")
val actualSig = parts[1].split("=")[1]
return MessageDigest.isEqual(expectedSig.toByteArray(), actualSig.toByteArray())
}
The hmacSha256 function uses HmacSHA256 from javax.crypto.Mac. Locally, using ngrok, the signatures match perfectly. But in our staging environment on AWS (us-east-2), the timestamp drift error triggers consistently, even though the NTP sync looks fine. Sometimes it passes, sometimes it fails for the exact same event type.
Is Genesys signing the payload differently for different regions? Or am I mishandling the v0 component? The docs say v0 is the HMAC of the timestamp and body, but I’m unsure if the body includes the raw POST string or if I need to normalize it. Any pointers on debugging this drift issue would be appreciated.