add signature verification

Author: KeithRyanWong

.fernignore

@@ -4,3 +4,4 @@ README.md
 assets/
 
 src/webflow/oauth.py
+src/webflow/signature.py

src/webflow/signature.py

@@ -0,0 +1,21 @@
+# If we can I'd like to move this to the webhooks client wrapper, 
+# but I can't find the Fern generation.yml to extend the client 
+# according to documentation included here:
+# https://buildwithfern.com/learn/sdks/capabilities/custom-code
+import hmac
+import hashlib
+from collections.abc import Mapping
+
+def verify(headers: Mapping, body:str , secret: str):
+    # Normalize header format to account for different server implementations
+    normalized_headers = {k.lower(): v for k, v in headers.items()}
+
+    message = f"{normalized_headers.get('x-webflow-timestamp', '')}:{body}".encode('utf-8')
+
+    generated_signature = hmac.new(
+        key=secret.encode('utf-8'),
+        msg=message,
+        digestmod=hashlib.sha256
+    ).hexdigest()
+
+    return normalized_headers.get("x-webflow-signature", "") == generated_signature