Use Ed25519 signatures for HTTP signatures

[aumetra]

I personally prefer Ed25519 over RSA and would like to not have to rely on it.

Blocked by https://github.com/mastodon/mastodon/issues/21429

[aumetra]

At least, in preparation for this change, we can add conditional public key parsing

[silverpill]

@aumetra Do you support actors having more than one key? For example, RSA and Ed25519. That would provide an upgrade path for Fediverse. Implementations may start generating Ed25519 keys for actors, while continuing to sign requests with RSA. When a critical mass is reached, we can switch to EdDSA signatures.

I have recently submitted a FEP that describes a possible solution: https://codeberg.org/fediverse/fep/src/branch/main/fep/521a/fep-521a.md.

[aumetra]

@silverpill Not yet but I was thinking about restructuring parts of the table that stores ActivityPub data in the future, so part of the restructure could be an 1:N relationship between actors and keys