Migrate authentication flow

[philipostli]

Authentication is moving to proprietary mouth provider and we need to add outh client to our authentication flow before the old endpoints are shut down.

https://docs.zaptec.com/page/upcoming-authentication-provider-migration#/

[PatrickE94]

We're already using the oauth password grant since 2 years back. We don't use any of the deprecated endpoints. We may consider the integrators method later on.