[pve-devel] [PATCH v2 proxmox-acme] support downloading alternate chains

[Fabian Grünbichler]

the current default chains end with an expired root certificate for
maximum compatibility with old Android versions. this breaks some other
older clients (openssl, gnutls) which don't expect chains to contain any
expired certificates, even if they are 'above' the trust anchor.

by setting $root, it is possible to specify which root the ACME provided
certificate chain should end with, downloading alternate chains as
necessary.

Signed-off-by: Fabian Grünbichler <f.gruenbichler at proxmox.com>
---

Notes:
    v2: 
    - only check issuer
    - also check default chain
    - add 'i' to RE check

    only tested with pebble

 src/PVE/ACME.pm | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/PVE/ACME.pm b/src/PVE/ACME.pm
index 265482d..57578d7 100644
--- a/src/PVE/ACME.pm
+++ b/src/PVE/ACME.pm
@@ -442,17 +442,50 @@ sub deactivate_authorization {
 
 # Get certificate
 # GET-as-POST to order's certificate URL
+# if $root is specified, attempts to find a matching (alternate) chain
 # Expects a '200 OK' reply
 # returns certificate chain in PEM format
 sub get_certificate {
-    my ($self, $order) = @_;
+    my ($self, $order, $root) = @_;
 
     $self->fatal("no certificate URL available (yet?)", $order)
        if !$order->{certificate};
 
+    my $check_root = sub {
+	my ($chain) = @_;
+
+	my @certs = PVE::Certificate::split_pem($chain);
+	my $root_pem = $certs[-1];
+
+	my ($file, $fh) = PVE::Tools::tempfile_contents($root_pem);
+	my $info = PVE::Certificate::get_certificate_info($file);
+
+	return defined($info->{issuer}) && $info->{issuer} =~ m/\Q$root\E/i;
+    };
+
     my $r = $self->do(POST => $order->{certificate}, '');
     my $return = eval {
+	# default chain
 	my $res = __get_result($r, 200, 1);
+	if ($root && !$check_root->($res)) {
+	    # alternate chains if requested and default didn't match
+	    $res = undef;
+	    my @links = $r->header('link');
+	    for my $link (@links) {
+		if ($link =~ /^<(.*)>;rel="alternate"$/) {
+		    my $url = $1;
+		    my $chain = eval { __get_result($self->do(POST => $url, ''), 200, 1); };
+		    die "failed to retrieve alternate chain from '$url' - $@\n" if $@;
+		    if ($check_root->($chain)) {
+			$res = $chain;
+			last;
+		    }
+		}
+	    }
+	    die "no matching alternate chain for '$root' returned by server\n"
+		if !defined($res);
+	}
+
 	if ($res =~ /^(-----BEGIN CERTIFICATE-----)(.+)(-----END CERTIFICATE-----)$/s) { # untaint
 	    return $1 . $2 . $3;
 	}
-- 
2.30.2