Implement default SignatureService and configuration values

[paullatzelsperger]

Feature Request

In order to enable proper remote signing of content we need the following things:

• a default SignatureService, that will perform signing locally by pulling keys from the default
• configuration values (as outlined in the decision record), to enable/disable remote signing, etc.
• a JWSSigner and a JWSVerifier implementation, which delegate signing to the SignatureService

Which Areas Would Be Affected?

hashicorp vault, default services

Why Is the Feature Desired?

make remote signing usable, plug it into JWT generation and validation.

Who will sponsor this feature?

Please @-mention the committer that will sponsor your feature.

Solution Proposal

If possible, provide a (brief!) solution proposal.