fix(framework) Clear node auth keys upon SuperLink start (#4736)

src/py/flwr/server/app.py

@@ -374,6 +374,7 @@ def run_superlink() -> None:
                     server_public_key,
                 ) = maybe_keys
                 state = state_factory.state()
+                state.clear_supernode_auth_keys_and_credentials()
                 state.store_node_public_keys(node_public_keys)
                 state.store_server_private_public_key(
                     private_key_to_bytes(server_private_key),

src/py/flwr/server/superlink/linkstate/in_memory_linkstate.py

@@ -430,6 +430,13 @@ def get_server_public_key(self) -> Optional[bytes]:
         """Retrieve `server_public_key` in urlsafe bytes."""
         return self.server_public_key
 
+    def clear_supernode_auth_keys_and_credentials(self) -> None:
+        """Clear stored `node_public_keys` and credentials in the link state if any."""
+        with self.lock:
+            self.server_private_key = None
+            self.server_public_key = None
+            self.node_public_keys.clear()
+
     def store_node_public_keys(self, public_keys: set[bytes]) -> None:
         """Store a set of `node_public_keys` in the link state."""
         with self.lock:

src/py/flwr/server/superlink/linkstate/linkstate.py

@@ -284,6 +284,10 @@ def get_server_private_key(self) -> Optional[bytes]:
     def get_server_public_key(self) -> Optional[bytes]:
         """Retrieve `server_public_key` in urlsafe bytes."""
 
+    @abc.abstractmethod
+    def clear_supernode_auth_keys_and_credentials(self) -> None:
+        """Clear stored `node_public_keys` and credentials in the link state if any."""
+
     @abc.abstractmethod
     def store_node_public_keys(self, public_keys: set[bytes]) -> None:
         """Store a set of `node_public_keys` in the link state."""

src/py/flwr/server/superlink/linkstate/linkstate_test.py

@@ -820,6 +820,29 @@ def test_store_server_private_public_key_twice(self) -> None:
                 new_private_key_bytes, new_public_key_bytes
             )
 
+    def test_clear_supernode_auth_keys_and_credentials(self) -> None:
+        """Test clear_supernode_auth_keys_and_credentials from linkstate."""
+        # Prepare
+        state: LinkState = self.state_factory()
+        key_pairs = [generate_key_pairs() for _ in range(3)]
+        public_keys = {public_key_to_bytes(pair[1]) for pair in key_pairs}
+
+        # Execute (store)
+        state.store_node_public_keys(public_keys)
+        private_key, public_key = generate_key_pairs()
+        private_key_bytes = private_key_to_bytes(private_key)
+        public_key_bytes = public_key_to_bytes(public_key)
+        state.store_server_private_public_key(private_key_bytes, public_key_bytes)
+
+        # Execute (clear)
+        state.clear_supernode_auth_keys_and_credentials()
+        node_public_keys = state.get_node_public_keys()
+
+        # Assert
+        assert node_public_keys == set()
+        assert state.get_server_private_key() is None
+        assert state.get_server_public_key() is None
+
     def test_node_public_keys(self) -> None:
         """Test store_node_public_keys and get_node_public_keys from state."""
         # Prepare

src/py/flwr/server/superlink/linkstate/sqlite_linkstate.py

@@ -818,6 +818,12 @@ def get_server_public_key(self) -> Optional[bytes]:
             public_key = None
         return public_key
 
+    def clear_supernode_auth_keys_and_credentials(self) -> None:
+        """Clear stored `node_public_keys` and credentials in the link state if any."""
+        queries = ["DELETE FROM public_key;", "DELETE FROM credential;"]
+        for query in queries:
+            self.query(query)
+
     def store_node_public_keys(self, public_keys: set[bytes]) -> None:
         """Store a set of `node_public_keys` in the link state."""
         query = "INSERT INTO public_key (public_key) VALUES (?)"