Cognito authentication in a secure VoD platform

Within a secure AWS video-on-demand platform, the goal is to authenticate users that can get access to content stored in s3.

If there is a different service for authenticating users, how can one integrate that with AWS? Will this be in addition to Cognito or replace Cognito with the other authenticator?

Are there specific steps to follow to accomplish this task?

This is the architecture diagram for aws service: https://aws.amazon.com/blogs/media/creating-a-secure-video-on-demand-vod-platform-using-aws/