Disable the backend UI
If you want the backend not to be accessible from the frontend site, you can disable the entire Sitefinity CMS backend UI. 
IMPORTANT: Disabling the backend UI will disable all routes starting with yoursite/Sitefinity. This includes all routes for Sitefinity CMS backend - /Sitefinity, all service routes - /Sitefinity/Services, routes for authentication/login and any other protected routes - /Sitefinity/<anything else>. Only the SiteSync and LoadBalancing modules routes will be allowed, if these modules are enabled in your site.
This scenario is useful if you have a load-balancing configuration and you want to disable the backend on all frontend nodes, but leave it enabled on nodes used for development. 
To disable the backend UI, perform the following:
    - Click Administration  Settings  Advanced  System.
- Select DisableBackendUI checkbox and click Save changes.
 This settings makes a change to the file ~/App-Data/Sitefinity/Configurations/SystemConfig.config by adding disableBackendUI="True"
- To enable the backend UI, open the SystemConfig.config and delete disableBackendUI="True"
 
NOTE: If you have a load balancing configuration, make sure that the SystemConfig.config is configured differently on the node where the backend is enabled and on the ones where the backend is disabled.