CkPython 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.

CkPython

import sys
import chilkat

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.
rawBody = chilkat.CkBinData()
success = rawBody.LoadFile("qa_data/box_webhook_body.bin")
if (success != True):
    print(rawBody.lastErrorText())
    sys.exit()

#  Read these fields case-insensitively from the incoming request headers.
#  For this offline example, enter the captured header values.
timestamp = "BOX_DELIVERY_TIMESTAMP"
primarySignature = "BOX_SIGNATURE_PRIMARY"
secondarySignature = "BOX_SIGNATURE_SECONDARY"
signatureVersion = "1"
signatureAlgorithm = "HmacSHA256"
#  Retrieve configured keys from protected application configuration.
primaryKey = "BOX_PRIMARY_SIGNATURE_KEY"
secondaryKey = "BOX_SECONDARY_SIGNATURE_KEY"
if ((signatureVersion != "1") or (signatureAlgorithm != "HmacSHA256")):
    print("Unsupported signature version or algorithm.")
    sys.exit()

delivered = chilkat.CkDateTime()
success = delivered.SetFromTimestamp(timestamp)
if (success != True):
    print(delivered.lastErrorText())
    sys.exit()

now = chilkat.CkDateTime()
success = now.SetFromCurrentSystemTime()
if (success != True):
    print(now.lastErrorText())
    sys.exit()

age = int(now.GetAsUnixTime(False)) - int(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) or (age < -60)):
    print("Delivery timestamp is outside the accepted window.")
    sys.exit()

signedBytes = chilkat.CkBinData()
success = signedBytes.AppendBd(rawBody)
if (success != True):
    print(signedBytes.lastErrorText())
    sys.exit()

success = signedBytes.AppendString(timestamp,"utf-8")
if (success != True):
    print(signedBytes.lastErrorText())
    sys.exit()

mac = chilkat.CkCrypt2()
mac.put_MacAlgorithm("hmac")
mac.put_HashAlgorithm("sha256")
mac.put_EncodingMode("base64")
success = mac.SetMacKeyString(primaryKey)
if (success != True):
    print(mac.lastErrorText())
    sys.exit()

expectedPrimary = mac.macBdENC(signedBytes)
if (mac.get_LastMethodSuccess() != True):
    print(mac.lastErrorText())
    sys.exit()

success = mac.SetMacKeyString(secondaryKey)
if (success != True):
    print(mac.lastErrorText())
    sys.exit()

expectedSecondary = mac.macBdENC(signedBytes)
if (mac.get_LastMethodSuccess() != True):
    print(mac.lastErrorText())
    sys.exit()

#  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.
random = chilkat.CkPrng()
comparisonKey = random.genRandom(32,"base64")
if (random.get_LastMethodSuccess() != True):
    print(random.lastErrorText())
    sys.exit()

success = mac.SetMacKeyEncoded(comparisonKey,"base64")
if (success != True):
    print(mac.lastErrorText())
    sys.exit()

pExpected = mac.macStringENC(expectedPrimary)
if (mac.get_LastMethodSuccess() != True):
    print(mac.lastErrorText())
    sys.exit()

pReceived = mac.macStringENC(primarySignature)
if (mac.get_LastMethodSuccess() != True):
    print(mac.lastErrorText())
    sys.exit()

sExpected = mac.macStringENC(expectedSecondary)
if (mac.get_LastMethodSuccess() != True):
    print(mac.lastErrorText())
    sys.exit()

sReceived = mac.macStringENC(secondarySignature)
if (mac.get_LastMethodSuccess() != True):
    print(mac.lastErrorText())
    sys.exit()

validPrimary = (primaryKey != "") and (primarySignature != "") and (pExpected == pReceived)
validSecondary = (secondaryKey != "") and (secondarySignature != "") and (sExpected == sReceived)
if ((validPrimary == False) and (validSecondary == False)):
    print("Signature verification failed.")
    sys.exit()

#  Parse JSON only after signature verification.
webhookEvent = chilkat.CkJsonObject()
success = webhookEvent.Load(rawBody.getString("utf-8"))
if (success != True):
    print(webhookEvent.lastErrorText())
    sys.exit()

print("Verified event ID: " + webhookEvent.stringOf("id"))
print("Trigger: " + webhookEvent.stringOf("trigger"))
#  Deduplicate using event.id, not BOX-DELIVERY-ID, which changes on retries.
#  Verify the target belongs to your configured webhook before dispatching work.