Add WebhookSignature.generate_test_header_string helper

stripe/_webhook.py

@@ -3,6 +3,7 @@
 import time
 from collections import OrderedDict
 from hashlib import sha256
+from typing import Optional
 
 # Used for global variables
 import stripe  # noqa: IMP101
@@ -39,6 +40,41 @@ def construct_event(
             )
         return event
 
+    @staticmethod
+    def generate_test_header_string(
+        payload: str,
+        secret: str,
+        timestamp: Optional[int] = None,
+        scheme: Optional[str] = None,
+        signature: Optional[str] = None,
+    ) -> str:
+        """
+        Generates a value for the `Stripe-Signature` header that can be used
+        when testing code that calls `Webhook.construct_event` or
+        `WebhookSignature.verify_header`. Mirrors `generateTestHeaderString`
+        from stripe-node.
+
+        Args:
+            payload: The webhook payload to sign, as a string.
+            secret: The webhook signing secret (`whsec_...`).
+            timestamp: Unix timestamp to embed in the header. Defaults to
+                the current time.
+            scheme: Signature scheme. Defaults to
+                `WebhookSignature.EXPECTED_SCHEME`.
+            signature: Pre-computed signature to embed in the header. If
+                omitted, a signature is computed from `payload` and `secret`.
+        """
+        if timestamp is None:
+            timestamp = int(time.time())
+        if scheme is None:
+            scheme = WebhookSignature.EXPECTED_SCHEME
+        if signature is None:
+            signed_payload = "%d.%s" % (timestamp, payload)
+            signature = WebhookSignature._compute_signature(
+                signed_payload, secret
+            )
+        return "t=%d,%s=%s" % (timestamp, scheme, signature)
+
 
 class WebhookSignature(object):
     EXPECTED_SCHEME = "v1"

tests/test_webhook.py

@@ -24,18 +24,13 @@
 
 
 def generate_header(**kwargs):
-    timestamp = kwargs.get("timestamp", int(time.time()))
-    payload = kwargs.get("payload", DUMMY_WEBHOOK_PAYLOAD)
-    secret = kwargs.get("secret", DUMMY_WEBHOOK_SECRET)
-    scheme = kwargs.get("scheme", stripe.WebhookSignature.EXPECTED_SCHEME)
-    signature = kwargs.get("signature", None)
-    if signature is None:
-        payload_to_sign = "%d.%s" % (timestamp, payload)
-        signature = stripe.WebhookSignature._compute_signature(
-            payload_to_sign, secret
-        )
-    header = "t=%d,%s=%s" % (timestamp, scheme, signature)
-    return header
+    return stripe.Webhook.generate_test_header_string(
+        payload=kwargs.get("payload", DUMMY_WEBHOOK_PAYLOAD),
+        secret=kwargs.get("secret", DUMMY_WEBHOOK_SECRET),
+        timestamp=kwargs.get("timestamp"),
+        scheme=kwargs.get("scheme"),
+        signature=kwargs.get("signature"),
+    )
 
 
 class TestWebhook(object):
@@ -149,6 +144,57 @@ def test_timestamp_off_but_no_tolerance(self):
         )
 
 
+class TestGenerateTestHeaderString(object):
+    def test_uses_defaults_when_optional_args_omitted(self):
+        before = int(time.time())
+        header = stripe.Webhook.generate_test_header_string(
+            payload=DUMMY_WEBHOOK_PAYLOAD, secret=DUMMY_WEBHOOK_SECRET
+        )
+        after = int(time.time())
+
+        parts = dict(item.split("=", 1) for item in header.split(","))
+        assert before <= int(parts["t"]) <= after
+        assert "v1" in parts
+
+    def test_header_verifies_round_trip(self):
+        header = stripe.Webhook.generate_test_header_string(
+            payload=DUMMY_WEBHOOK_PAYLOAD, secret=DUMMY_WEBHOOK_SECRET
+        )
+        assert stripe.WebhookSignature.verify_header(
+            DUMMY_WEBHOOK_PAYLOAD,
+            header,
+            DUMMY_WEBHOOK_SECRET,
+            tolerance=10,
+        )
+
+    def test_honors_custom_timestamp_and_scheme(self):
+        header = stripe.Webhook.generate_test_header_string(
+            payload=DUMMY_WEBHOOK_PAYLOAD,
+            secret=DUMMY_WEBHOOK_SECRET,
+            timestamp=12345,
+            scheme="v0",
+        )
+        assert header.startswith("t=12345,v0=")
+
+    def test_uses_provided_signature_verbatim(self):
+        header = stripe.Webhook.generate_test_header_string(
+            payload=DUMMY_WEBHOOK_PAYLOAD,
+            secret=DUMMY_WEBHOOK_SECRET,
+            timestamp=12345,
+            signature="deadbeef",
+        )
+        assert header == "t=12345,v1=deadbeef"
+
+    def test_bad_secret_fails_verification(self):
+        header = stripe.Webhook.generate_test_header_string(
+            payload=DUMMY_WEBHOOK_PAYLOAD, secret="whsec_wrong"
+        )
+        with pytest.raises(SignatureVerificationError):
+            stripe.WebhookSignature.verify_header(
+                DUMMY_WEBHOOK_PAYLOAD, header, DUMMY_WEBHOOK_SECRET
+            )
+
+
 class TestStripeClientConstructEvent(object):
     def test_construct_event(self, stripe_mock_stripe_client):
         header = generate_header()