@mtsb From the top of my head:
• RESTlet = TBA.
• Suitelet = Regular Auth which mean you will need to somehow get the active session/cookie and use that to call the second Suitelet.
So you have basically two options:
1- Available without login.
2- Make it a RESTlet.
For available without login you can create some hash that you recreate and compare in the second suitelet for security purposes.
N/crypto