OAuth
Why it matters for creators
OAuth is the flow you have used a hundred times without naming it: the screen that appears when you connect an account, lists what the app is asking for, and returns you afterwards.
The important property is where you type your password, which is on Instagram's own page, not the app's. The tool never sees it, never stores it, and could not use it if it wanted to. What it receives is an access token scoped to the specific permissions shown on that screen.
This gives you a straightforward test for any tool asking to connect to your Instagram. If it hands you off to Instagram to log in, it is doing this correctly. If it asks for your Instagram username and password in its own form, it is not using OAuth, which means it is not using the official Graph API either, and the account is at risk regardless of how the product looks.