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[Python] Make the webhook tolerance configurable. #2055

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[Python] Make the webhook tolerance configurable. #2055

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8bcae65
Update python sdk to allow a configurable webhook tolerance.
ogenodisho Sep 4, 2025
e69d025
Merge branch 'main' into feature/python-webhook-custom-tolerance
ogenodisho Sep 5, 2025
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10 changes: 6 additions & 4 deletions python/svix/webhooks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,9 @@ class WebhookVerificationError(Exception):
class Webhook:
_SECRET_PREFIX: str = "whsec_"
_whsecret: bytes
_whtolerance: timedelta

def __init__(self, whsecret: t.Union[str, bytes]):
def __init__(self, whsecret: t.Union[str, bytes], whtolerance: timedelta = timedelta(minutes=5)):
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I think a better approach would be adding the VerifyIgnoringTimestamp method, like we have in Go, as it was discussed in #93

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My concern with this is that it might make it 'easy' to use potentially insecure tolerances. With a separate method it's clear that the security implications are different.

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@ogenodisho ogenodisho Sep 5, 2025 •
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Hi @svix-lucho, thanks for the review.

I did see that part in the related issue about verifying the webhook while ignoring the timestamp. However, my reasoning for doing it this way is that I think it's actually safer (and more flexible) than allowing consumers to disable the timestamp verification entirely.

If a consumer disables it entirely, they're much more susceptible to replay attacks. However, if the tolerance is configurable, they have the flexibility of tuning the tolerance to suit their use cases, while still being protected against potential replay attacks to a certain degree.

In regards to your second message, I wouldn't be opposed to introducing a verify_using_custom_tolerance method instead.

Please let me know your thoughts.

if not whsecret:
raise RuntimeError("Secret can't be empty.")

Expand All @@ -30,6 +31,8 @@ def __init__(self, whsecret: t.Union[str, bytes]):

if isinstance(whsecret, bytes):
self._whsecret = whsecret

self._whtolerance = whtolerance

def verify(self, data: t.Union[bytes, str], headers: t.Dict[str, str]) -> t.Any:
data = data if isinstance(data, str) else data.decode()
Expand Down Expand Up @@ -67,15 +70,14 @@ def sign(self, msg_id: str, timestamp: datetime, data: str) -> str:
return f"v1,{base64.b64encode(signature).decode('utf-8')}"

def __verify_timestamp(self, timestamp_header: str) -> datetime:
webhook_tolerance = timedelta(minutes=5)
now = datetime.now(tz=timezone.utc)
try:
timestamp = datetime.fromtimestamp(float(timestamp_header), tz=timezone.utc)
except Exception:
raise WebhookVerificationError("Invalid Signature Headers")

if timestamp < (now - webhook_tolerance):
if timestamp < (now - self._whtolerance):
raise WebhookVerificationError("Message timestamp too old")
if timestamp > (now + webhook_tolerance):
if timestamp > (now + self._whtolerance):
raise WebhookVerificationError("Message timestamp too new")
return timestamp
15 changes: 15 additions & 0 deletions python/tests/test_webhooks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -177,3 +177,18 @@ def test_sign_function():
wh = Webhook(key)
signature = wh.sign(msg_id=msg_id, timestamp=timestamp, data=payload)
assert signature == expected


def test_default_tolerance_is_five_minutes():
testPayload = PayloadForTesting()
wh = Webhook(testPayload.secret)

assert wh._whtolerance == timedelta(minutes=5)


def test_custom_tolerance_is_set():
testPayload = PayloadForTesting()
custom_tolerance = timedelta(minutes=10)
wh = Webhook(testPayload.secret, custom_tolerance)

assert wh._whtolerance == custom_tolerance