[pbs-devel] [PATCH proxmox-backup v2 1/1] fix #6939: acme: accept HTTP 204 from newNonce endpoint

[Samuel Rufinatscha]

When registering an ACME account, PBS fetches a fresh nonce by issuing a
HEAD request to the server's newNonce URL. Until now we assumed this
request would return HTTP 200 OK.

In practice, some ACME servers [1] respond with HTTP 204 No Content for
this HEAD request while still providing a valid Replay-Nonce header.
This causes PBS to abort registration with "ACME server responded with
unexpected status code: 204", even though the server would otherwise
issue certificates correctly. This behavior is technically
off-spec [2], however not forbidden.

Adjust the ACME client code in PBS to accept both 200 OK and 204 No
Content as successful results for the newNonce step. We continue to
reject other status codes so we don't silently accept arbitrary 2xx
responses.

Note: In comparison, PVE’s Perl ACME client performs a GET request [3]
instead of a HEAD request and accepts any 2xx success code when
retrieving the nonce [4]. This difference in behavior does not affect
functionality but is worth noting for consistency across
implementations.

[1] https://bugzilla.proxmox.com/show_bug.cgi?id=6939
[2] https://datatracker.ietf.org/doc/html/rfc8555/#section-7.2
[3] https://git.proxmox.com/?p=proxmox-acme.git;a=blob;f=src/PVE/ACME.pm;h=f1e9bb7d316e3cea1e376c610b0479119217aecc;hb=HEAD#l219
[4] https://git.proxmox.com/?p=proxmox-acme.git;a=blob;f=src/PVE/ACME.pm;h=f1e9bb7d316e3cea1e376c610b0479119217aecc;hb=HEAD#l597

Fixes: #6939
Signed-off-by: Samuel Rufinatscha <s.rufinatscha at proxmox.com>
---
 src/acme/client.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/acme/client.rs b/src/acme/client.rs
index 1c12a4b9..7c32940b 100644
--- a/src/acme/client.rs
+++ b/src/acme/client.rs
@@ -15,7 +15,7 @@ use serde::{Deserialize, Serialize};
 use proxmox_acme::account::AccountCreator;
 use proxmox_acme::order::{Order, OrderData};
 use proxmox_acme::types::AccountData as AcmeAccountData;
-use proxmox_acme::Request as AcmeRequest;
+use proxmox_acme::{http_success, Request as AcmeRequest};
 use proxmox_acme::{Account, Authorization, Challenge, Directory, Error, ErrorResponse};
 use proxmox_http::client::Client;
 use proxmox_sys::fs::{replace_file, CreateOptions};
@@ -530,7 +530,7 @@ impl AcmeClient {
         };
 
         if parts.status.is_success() {
-            if status != request.expected {
+            if !request.expected.contains(&status) {
                 return Err(Error::InvalidApi(format!(
                     "ACME server responded with unexpected status code: {:?}",
                     parts.status
@@ -609,7 +609,7 @@ impl AcmeClient {
                 method: "GET",
                 content_type: "",
                 body: String::new(),
-                expected: 200,
+                expected: &[http_success::OK],
             },
             nonce,
         )
@@ -657,7 +657,7 @@ impl AcmeClient {
                 method: "HEAD",
                 content_type: "",
                 body: String::new(),
-                expected: 200,
+                expected: &[http_success::OK, http_success::NO_CONTENT],
             },
             nonce,
         )
-- 
2.47.3