Don't leak internal verifier errors to RPC clients

The _DashboardAuthInterceptor was passing raw ValueError messages
(e.g. "Invalid token: Not enough segments") to ConnectError. Use a
generic "Authentication failed" message for invalid tokens (matching
AuthInterceptor behavior) and log the detail server-side.

Author: rjpower

lib/iris/src/iris/cluster/controller/dashboard.py

@@ -199,7 +199,10 @@ def intercept_unary_sync(self, call_next, request, ctx):
             from connectrpc.code import Code
             from connectrpc.errors import ConnectError
 
-            raise ConnectError(Code.UNAUTHENTICATED, str(exc)) from exc
+            if token is None:
+                raise ConnectError(Code.UNAUTHENTICATED, str(exc)) from exc
+            logger.warning("Authentication failed: %s", exc)
+            raise ConnectError(Code.UNAUTHENTICATED, "Authentication failed") from exc
 
         if identity is None:
             # Optional mode, no token — anonymous fallback.