Is it possible to generate a JWT token for google in Kotlin, or are there other ways to authorize in Google Storage?

Question

Android

We languished for a very long time.
There is Google Storage, access to which must be made by an authorized user in the background.
Accesses via separate API keys are not set for them (checked)
Oauth2.0 was tried, but authorization crashes there with a suggestion to select an account for the user, authorization is needed without asking the user (i.e. our account) suffered and did not understand how to do it.
We found a JWT with a service account to generate and then exchange it for a bearer, everything works, but it was not possible to sign (that is, it was not possible to encode all the fields from under Kotlin.)
Has anyone cooked in this kitchen?