Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: pontemonti

libraries/microsoft-agents-a365-tooling-extensions-openai/microsoft_agents_a365/tooling/extensions/openai/mcp_tool_registration_service.py

@@ -88,7 +88,7 @@ async def add_tool_servers_to_agent(
             New Agent instance with all MCP servers, or original agent if no new servers
         """
 
-        if auth_token is None:
+        if auth_token is None or auth_token.strip() == "":
             scopes = get_mcp_platform_authentication_scope()
             authToken = await auth.exchange_token(context, scopes, auth_handler_name)
             auth_token = authToken.token