Implement or use an Authenticator

[rainerschoe]

Tokens will expire. We need to make sure we get new tokens on demand.
Go implementation uses the Authenticator:
https://github.com/IBM/go-sdk-core/blob/main/Authentication.md

There exists an archived rust version:
https://github.com/IBM/rust-sdk-core

but maybe we can implement a trivial lightweight version on our own.

[jgsogo]

Is APIKey encryption relevant? https://github.com/IBM/appconfiguration-js-client-sdk/blob/main/README_APIKEY_ENCRYPTION.md

[rainerschoe]

Is APIKey encryption relevant? https://github.com/IBM/appconfiguration-js-client-sdk/blob/main/README_APIKEY_ENCRYPTION.md

From how I read this document, I think this is a requirement for JS only.