Hi Harisanker,
Your current design seems already quite nice. I'm also hesistent in allowing anonymous users into a Mendix app, so I'd like to share an alternative here.
You could publish an API using the Published REST Service functionality. Large parts of your current setup can be reused, as you still need the binary within Mendix as FileDocument. See this documentation where Mendix describes a CMS system in Mendix, which is somewhat similar to your needs.
You can add any path or query parameter for the full security. My recommendations:
See for more deepdive into using obfuscated URLs for confidential data here.
Good luck!
Johan