debug: Gather more context and report exceptions on signature issues (#54464)

Unsubscribe notification signatures aren't working in saas, but they do
seem to work locally and in s4s. Currently difficult to determine the
source causes, so trying to capture an exception here with additional
context for debugging purposes.

Author: corps

src/sentry/utils/linksign.py

@@ -4,6 +4,7 @@
 
 from django.core import signing
 from django.urls import reverse
+from sentry_sdk.api import capture_exception
 
 from sentry import options
 from sentry.models import User
@@ -50,10 +51,15 @@ def process_signature(request, max_age=60 * 60 * 24 * 10):
     if not sig or sig.count(":") < 2:
         return None
 
-    signed_data = "{}|{}|{}".format(request.build_absolute_uri("/").rstrip("/"), request.path, sig)
+    request_absolute_uri = request.build_absolute_uri("/").rstrip("/")
+    request_path = request.path
+    signed_data = f"{request_absolute_uri}|{request_path}|{sig}"
     try:
         data = get_signer().unsign(signed_data, max_age=max_age)
-    except signing.BadSignature:
+    except signing.BadSignature as e:
+        # We should plan on removing this after debugging the current issue -- it is an 'expected' exception and not
+        # actually exceptional.
+        capture_exception(e)
         return None
 
     _, signed_path, user_id = data.rsplit("|", 2)