C++ Requires Chilkat v11.5.0+

Box: Verify a Captured V2 Webhook Signature

See more Box Examples

Verify raw payload bytes and captured headers using the configured primary and secondary signing keys. The example rejects stale/future timestamps and compares randomized HMACs of the signatures to avoid exposing a signature-prefix timing comparison. It does not host an HTTP listener. The receiver must persist/deduplicate the verified event and acknowledge promptly.

See the Box API guide for setup and the complete workflow.

C++

#include <CkBinData.h>
#include <CkDateTime.h>
#include <CkCrypt2.h>
#include <CkPrng.h>
#include <CkJsonObject.h>

void ChilkatSample(void)
    {
    bool success = false;

    //  Requires Chilkat 11.5.0 or later and a previously unlocked Chilkat bundle.
    //  See Global Unlock Sample.
    //  Guide: Box API Guide.

    success = false;

    //  Save the exact HTTP body bytes to this file, without JSON reserialization.
    CkBinData rawBody;
    success = rawBody.LoadFile("qa_data/box_webhook_body.bin");
    if (success != true) {
        std::cout << rawBody.lastErrorText() << "\r\n";
        return;
    }

    //  Read these fields case-insensitively from the incoming request headers.
    //  For this offline example, enter the captured header values.
    const char *timestamp = "BOX_DELIVERY_TIMESTAMP";
    const char *primarySignature = "BOX_SIGNATURE_PRIMARY";
    const char *secondarySignature = "BOX_SIGNATURE_SECONDARY";
    const char *signatureVersion = "1";
    const char *signatureAlgorithm = "HmacSHA256";
    //  Retrieve configured keys from protected application configuration.
    const char *primaryKey = "BOX_PRIMARY_SIGNATURE_KEY";
    const char *secondaryKey = "BOX_SECONDARY_SIGNATURE_KEY";
    if ((signatureVersion != "1") || (signatureAlgorithm != "HmacSHA256")) {
        std::cout << "Unsupported signature version or algorithm." << "\r\n";
        return;
    }

    CkDateTime delivered;
    success = delivered.SetFromTimestamp(timestamp);
    if (success != true) {
        std::cout << delivered.lastErrorText() << "\r\n";
        return;
    }

    CkDateTime now;
    success = now.SetFromCurrentSystemTime();
    if (success != true) {
        std::cout << now.lastErrorText() << "\r\n";
        return;
    }

    int age = atoi(now.GetAsUnixTime(false)) - atoi(delivered.GetAsUnixTime(false));
    //  Box recommends rejecting deliveries older than ten minutes.
    //  Allow at most 60 seconds of future clock skew; keep the server clock synchronized.
    if ((age > 600) || (age < -60)) {
        std::cout << "Delivery timestamp is outside the accepted window." << "\r\n";
        return;
    }

    CkBinData signedBytes;
    success = signedBytes.AppendBd(rawBody);
    if (success != true) {
        std::cout << signedBytes.lastErrorText() << "\r\n";
        return;
    }

    success = signedBytes.AppendString(timestamp,"utf-8");
    if (success != true) {
        std::cout << signedBytes.lastErrorText() << "\r\n";
        return;
    }

    CkCrypt2 mac;
    mac.put_MacAlgorithm("hmac");
    mac.put_HashAlgorithm("sha256");
    mac.put_EncodingMode("base64");
    success = mac.SetMacKeyString(primaryKey);
    if (success != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    const char *expectedPrimary = mac.macBdENC(signedBytes);
    if (mac.get_LastMethodSuccess() != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    success = mac.SetMacKeyString(secondaryKey);
    if (success != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    const char *expectedSecondary = mac.macBdENC(signedBytes);
    if (mac.get_LastMethodSuccess() != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    //  Blind both sides with a fresh secret random key before equality comparison.
    //  Never compare the original HMAC strings using a prefix-short-circuit comparison.
    //  A host-language receiver can instead use its standard constant-time byte comparison.
    CkPrng random;
    const char *comparisonKey = random.genRandom(32,"base64");
    if (random.get_LastMethodSuccess() != true) {
        std::cout << random.lastErrorText() << "\r\n";
        return;
    }

    success = mac.SetMacKeyEncoded(comparisonKey,"base64");
    if (success != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    const char *pExpected = mac.macStringENC(expectedPrimary);
    if (mac.get_LastMethodSuccess() != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    const char *pReceived = mac.macStringENC(primarySignature);
    if (mac.get_LastMethodSuccess() != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    const char *sExpected = mac.macStringENC(expectedSecondary);
    if (mac.get_LastMethodSuccess() != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    const char *sReceived = mac.macStringENC(secondarySignature);
    if (mac.get_LastMethodSuccess() != true) {
        std::cout << mac.lastErrorText() << "\r\n";
        return;
    }

    bool validPrimary = (primaryKey != "") && (primarySignature != "") && (pExpected == pReceived);
    bool validSecondary = (secondaryKey != "") && (secondarySignature != "") && (sExpected == sReceived);
    if ((validPrimary == false) && (validSecondary == false)) {
        std::cout << "Signature verification failed." << "\r\n";
        return;
    }

    //  Parse JSON only after signature verification.
    CkJsonObject webhookEvent;
    success = webhookEvent.Load(rawBody.getString("utf-8"));
    if (success != true) {
        std::cout << webhookEvent.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Verified event ID: " << webhookEvent.stringOf("id") << "\r\n";
    std::cout << "Trigger: " << webhookEvent.stringOf("trigger") << "\r\n";
    //  Deduplicate using event.id, not BOX-DELIVERY-ID, which changes on retries.
    //  Verify the target belongs to your configured webhook before dispatching work.
    }