This PR is part of https://codeberg.org/forgejo/forgejo/pulls/4767
It improves the signature handling:
1. move logic to a service (might be used from other services as well)
2. make a clear difference between ` ReqHTTPUserSignature` and `ReqHTTPUserOrInstanceSignature`
3. improve test ability (activitypub/client & distant_federation_server_mock
Adjust instance actor
1. name &
2. webfinger
## Strategy for next PRs is
Integration tests are in the driving seat.
I will step by step add integration tests form original PR and add code required by the integration test changes.
## Meta
Proposal howto process large PRs can be discussed here: https://codeberg.org/forgejo-contrib/federation/pulls/37
Current state with rendered diagrams can be found here: https://codeberg.org/meissa/federation/src/branch/merge-large-pr/doc/merge-large-pr.md
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8275
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
Co-committed-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
