[Request] Create callback for using externally managed key material/identities

[Aconitin]

Description

Since we manage our own identities, all operations that involve key material must be deferable to our backend, e.g. verifying signatures.

Motivation

We manage our own identities and also use certain different DID methods that UniCore is unable to resolve by itself.

Requirements

Use UniCore event system ("callbacks") for all key operations and resolve operations (or all operations involving resolution).

Open Questions

No response

Are you planning to contribute this in a PR?

No