Nicoo hello and welcome !
Are you trying to add your own additional controls inside Flarum ? In this case you're looking at extensions. We have the official docs (some parts still being written) https://flarum.org/docs/extend/ and many example extensions. If you're stuck let us know what you're trying to achieve and we can find extensions that do similar things to yours, so you can get inspiration.
If you're trying to use Flarum as a login provider or to control parts of Flarum from another application, have a look at the Flarum REST API (unfortunately I don't know if we have any docs about that from a non-extension perspective).
If you try to sync passwords with another service, Flarum uses bycrypt for the hashes.
