API calls in a federal user Azure Setup?

Hi,

I'm really struggling in using the pbi API. Checked nearly every tutorial existing but i'm stuck with our setup: Azure AD with synced user & Okta & 2FA. So basically AAD is not aware of my users password - and therefore I can't use the normal method :(

I tried several things:

Following best practice here - response is "AADSTS50056 Invalid or null password -Password does not exist in store for this user.". Makes sense as AAD is not aware of my password.

So I tried with grant_type: client_credentials. With this I'm able to get a bearer token. But when I use this token for the pbi call i'm getting an 403 unautorized response. Which also makes sense in some way as I never stated my user/password. 

Any help/postman examples would be really helpful! 

Thanks :)