You use Intune to log in and register your device against your Microsoft account, and microsoft-identity-broker is a DBus service that hands out tokens that can be passed to login.microsoft.com (either as a cookie or a special header) which identifies you (skipping the username/password login) and allows you to pass the company device test.
I was able to put together a working ad-hoc extension for Firefox to make the DBus call and pass the header, though I've since come across this extension (haven't tried it myself) which looks like it achieves the same thing (with a lot more features, based on the code size?):
https://github.com/siemens/linux-entra-sso
Edge on Linux seems to have this built in, so if you open any page on login.microsoft.com, you'll see it passing some "x-something" header with a token that it receieved from the identity broker (generated on each page load).