The mail-auth crate doesn't support 1024 bit RSA keys, which are
currently the dominant size of key used by senders at scale.
It is not possible to even configure a 2048 bit RSA key in some DNS
providers, which blocks widespread adoption of larger key sizes.
This commit pulls in the cfdkim crate as an alternative implementation.
I'm not happy with this implementation because the API of the crate
defeats some caching optimizations, doesn't support certain signing
attributes that are supported by mail-auth and the generated header isn't
nicely wrapped.
We'll likely "do something" to resolve this in a future commit.
For now, this implementation is enabled by setting `use_cf = true`
in the signing parameters.
it pulls in an old version of the time crate that flags many
rust projects as being vulnerable to an old CVE.
We still have other references to time that I'll remove in a follow up.
A fairly sprawling commit:
* Move config to its own crate to facilitate making things more modular
* Crates/modules can now provide a registration function that can be
used to setup functions in the lua environment
* Message crate now has a dkim module with a signer type that can
be loaded from lua; signers are cached (with ttl) and shareable
* Message now has a dkim_sign method that does the signing, as well
as methods for appending and prepending headers that are necessary
to support signing.
* Switch uuids to v1 format, so that we can cheaply determine
when a message was created without having to load its metadata
from the spool
* Add some message delivery parameters; retry interval, limit, max age
* Respect those parameters when spooling in and when we encounter
a transient failure.
Wez Furlong