fix: clarify feature flag auth errors

.sampo/changesets/feature-flag-auth-errors.md

@@ -0,0 +1,5 @@
+---
+pypi/posthog: patch
+---
+
+Improve local feature flag authentication error messages.

posthog/client.py

@@ -1353,9 +1353,12 @@ def _fetch_feature_flags_from_api(self):
 
         except APIError as e:
             if e.status == 401:
-                self.log.error(
-                    "[FEATURE FLAGS] Error loading feature flags: To use feature flags, please set a valid personal_api_key. More information: https://posthog.com/docs/api/overview"
+                detail = (
+                    f"Error loading feature flags: {e.message}. "
+                    "Please verify both your project_api_key and personal_api_key. "
+                    "More information: https://posthog.com/docs/api/overview"
                 )
+                self.log.error("[FEATURE FLAGS] %s", detail)
                 self.feature_flags = []
                 self.group_type_mapping = {}
                 self.cohorts = {}
@@ -1364,12 +1367,7 @@ def _fetch_feature_flags_from_api(self):
                     self.flag_cache.clear()
 
                 if self.debug:
-                    raise APIError(
-                        status=401,
-                        message="You are using a write-only key with feature flags. "
-                        "To use feature flags, please set a personal_api_key "
-                        "More information: https://posthog.com/docs/api/overview",
-                    )
+                    raise APIError(status=401, message=detail)
             elif e.status == 402:
                 self.log.warning(
                     "[FEATURE FLAGS] PostHog feature flags quota limited, resetting feature flag data.  Learn more about billing limits at https://posthog.com/docs/billing/limits-alerts"

posthog/test/test_client.py

@@ -555,7 +555,9 @@ def test_load_feature_flags_unauthorized(self, patch_get):
             self.assertEqual(client.feature_flags_by_key, {})
             self.assertEqual(client.group_type_mapping, {})
             self.assertEqual(client.cohorts, {})
-            self.assertIn("please set a valid personal_api_key", logs.output[0])
+            self.assertIn("Unauthorized", logs.output[0])
+            self.assertIn("project_api_key", logs.output[0])
+            self.assertIn("personal_api_key", logs.output[0])
 
     @mock.patch("posthog.client.flags")
     def test_dont_override_capture_with_local_flags(self, patch_flags):

posthog/test/test_feature_flags.py

@@ -2546,12 +2546,12 @@ def test_load_feature_flags_wrong_key(self, patch_get, _patch_poll):
 
         with self.assertLogs("posthog", level="ERROR") as logs:
             client.load_feature_flags()
-            self.assertEqual(
-                logs.output[0],
-                "ERROR:posthog:[FEATURE FLAGS] Error loading feature flags: To use feature flags, please set a valid personal_api_key. More information: https://posthog.com/docs/api/overview",
-            )
+            self.assertIn("Unauthorized", logs.output[0])
+            self.assertIn("project_api_key", logs.output[0])
+            self.assertIn("personal_api_key", logs.output[0])
         client.debug = True
-        self.assertRaises(APIError, client.load_feature_flags)
+        with self.assertRaisesRegex(APIError, "Unauthorized"):
+            client.load_feature_flags()
 
     @mock.patch("posthog.client.flags")
     @mock.patch("posthog.client.get")