Hey @Sadman Sakib , thank you for reaching out!
The authentication token would be the JWT token. When you are using DRM to protect your videos, you will be creating streaming locators with proper streaming policy stream-streaming-policy-concept and Content Key Policy drm-content-key-policy-concept. The content key policy has claims and private key that you need to configure while creating it.
When someone is trying to view a DRM protected video, you should be generating a JWT token with same claims as the Content Key Policy, and make sure to sign the signature with the same private key. For more information you can check AMS documentation here drm-content-protection-concept it also has some good samples about how to generate the JWT token.