fix: correct user info loading in apple backend

incorrect function was used for parsing json (load is for files, loads for strings)
and the error was masked because of too broad except clause

Author: melanger

src/satosa/backends/apple.py

@@ -76,8 +76,8 @@ def response_endpoint(self, context, *args):
         # - https://developer.apple.com/documentation/sign_in_with_apple/namei
         try:
             userdata = context.request.get("user", "{}")
-            userinfo = json.load(userdata)
-        except Exception:
+            userinfo = json.loads(userdata)
+        except json.JSONDecodeError:
             userinfo = {}
 
         authn_resp = self.client.parse_response(