accountd: Pass JWA and JWK thumbprint via extended greeting data.

Passing the JWA to the ACME client is required if we want to support
account keys other than RSA.  As of 0.7 both lacme-accountd(1) and
lacme(8) hardcode “RS256” (SHA256withRSA per RFC 7518 sec. A.1).

Passing the JWK thumbprint is handy as it gives more flexibility if RFC
8555 sec. 8.1 were to be updated with another digest algorithm (it's
currently hardcoded to SHA-256).  A single lacme-account(1) instance
might be used to sign requests from many clients, and it's easier to
upgrade a single ‘lacme-accountd’ than many ‘lacme’.  Moreover, in some
restricted environments lacme-accountd might hide the JWK from the
client to prevent ‘newAccount’ requests (such as contact updates);
passing its thumbprint is enough for ‘newOrder’ requests.

1 files changed, 2 insertions, 0 deletions

diff --git a/Changelog b/Changelog
index e6becda..ffd9536 100644
--- a/Changelog
+++ b/Changelog
@@ -69,6 +69,8 @@ lacme (0.7.1) upstream;
    connection through ssh.  The new flag is documented to allow safe
    usage is authorized_keys(5) restrictions.
  + Remove dependency on List::Util (core module).
+ + accountd: Pass JWA and JWK thumbprint via extended greeting data.
+   This gives better forward flexibility.
  - lacme: delay webserver socket shutdown to after the process has
    terminated.
  - documentation: suggest to generate private key material with