No downloads, no installs, no subscriptions, pay as you play, and enjoy anonymous surfing and secure collaboration. For example, a daily script that checks emails from certain contacts and sends automated responses The article explains setting up app only principal access to sharepoint online sites using azure ad application registration.
SharePoint App-Only Authentication
Unlock sharepoint's true potential and navigate domains seamlessly
It’s usually the right choice if
The application needs to run in an automated way, without user input
