Add async-support for loading the keys from storage and async-operations for the seed store.
Proposed design-change for TokenGenerator and TokenVerifier:
to pass keys in each public method instead of the class-constructor. Reason is that the keys are loaded asynchronously and we can't use async-methods in constructors. Didn't find other suitable techniques since we don't allow initial null-values (making lazy-loading them per-use not an option either).
Add async-support for loading the keys from storage and async-operations for the seed store.
Proposed design-change for
TokenGeneratorandTokenVerifier: