acme: Add csr option (#376334)

nixos/doc/manual/release-notes/rl-2505.section.md

···
   They are still expected to be working until future version 5.0.0, but will generate warnings in logs.
   Read the [release notes](https://www.authelia.com/blog/4.39-release-notes/) for human readable summaries of the changes.
 
+- `security.acme` now supports renewal using CSRs (Certificate Signing Request) through the options `security.acme.*.csr` and `security.acme.*.csrKey`.
+
 - `programs.fzf.keybindings` now supports the fish shell.
 
 - `gerbera` now has wavpack support.

nixos/modules/security/acme/default.nix

···
 
       # Create hashes for cert data directories based on configuration
       # Flags are separated to avoid collisions
-      hashData = with builtins; ''
-        ${lib.concatStringsSep " " data.extraLegoFlags} -
-        ${lib.concatStringsSep " " data.extraLegoRunFlags} -
-        ${lib.concatStringsSep " " data.extraLegoRenewFlags} -
-        ${toString acmeServer} ${toString data.dnsProvider}
-        ${toString data.ocspMustStaple} ${data.keyType}
-      '';
+      hashData =
+        with builtins;
+        ''
+          ${lib.concatStringsSep " " data.extraLegoFlags} -
+          ${lib.concatStringsSep " " data.extraLegoRunFlags} -
+          ${lib.concatStringsSep " " data.extraLegoRenewFlags} -
+          ${toString acmeServer} ${toString data.dnsProvider}
+          ${toString data.ocspMustStaple} ${data.keyType}
+        ''
+        + (lib.optionalString (data.csr != null) (" - " + data.csr));
       certDir = mkHash hashData;
       # TODO remove domainHash usage entirely. Waiting on go-acme/lego#1532
       domainHash = mkHash "${lib.concatStringsSep " " extraDomains} ${data.domain}";
···
           "--accept-tos" # Checking the option is covered by the assertions
           "--path"
           "."
-          "-d"
-          data.domain
           "--email"
           data.email
-          "--key-type"
-          data.keyType
         ]
         ++ protocolOpts
         ++ lib.optionals (acmeServer != null) [
           "--server"
           acmeServer
         ]
+        ++ lib.optionals (data.csr != null) [
+          "--csr"
+          data.csr
+        ]
+        ++ lib.optionals (data.csr == null) [
+          "--key-type"
+          data.keyType
+          "-d"
+          data.domain
+        ]
         ++ lib.concatMap (name: [
           "-d"
           name
···
       webroots = lib.remove null (
         lib.unique (builtins.map (certAttrs: certAttrs.webroot) (lib.attrValues config.security.acme.certs))
       );
+
+      certificateKey = if data.csrKey != null then "${data.csrKey}" else "certificates/${keyName}.key";
     in
     {
       inherit accountHash cert selfsignedDeps;
···
           # Check if we can renew.
           # We can only renew if the list of domains has not changed.
           # We also need an account key. Avoids #190493
-          if cmp -s domainhash.txt certificates/domainhash.txt && [ -e 'certificates/${keyName}.key' ] && [ -e 'certificates/${keyName}.crt' ] && [ -n "$(find accounts -name '${data.email}.key')" ]; then
+          if cmp -s domainhash.txt certificates/domainhash.txt && [ -e '${certificateKey}' ] && [ -e 'certificates/${keyName}.crt' ] && [ -n "$(find accounts -name '${data.email}.key')" ]; then
 
             # Even if a cert is not expired, it may be revoked by the CA.
             # Try to renew, and silently fail if the cert is not expired.
···
             touch out/renewed
             echo Installing new certificate
             cp -vp 'certificates/${keyName}.crt' out/fullchain.pem
-            cp -vp 'certificates/${keyName}.key' out/key.pem
+            cp -vp '${certificateKey}' out/key.pem
             cp -vp 'certificates/${keyName}.issuer.crt' out/chain.pem
             ln -sf fullchain.pem out/cert.pem
             cat out/key.pem out/fullchain.pem > out/full.pem
···
           description = "Domain to fetch certificate for (defaults to the entry name).";
         };
 
+        csr = lib.mkOption {
+          type = lib.types.nullOr lib.types.str;
+          default = null;
+          description = "Path to a certificate signing request to apply when fetching the certificate.";
+        };
+
+        csrKey = lib.mkOption {
+          type = lib.types.nullOr lib.types.str;
+          default = null;
+          description = "Path to the private key to the matching certificate signing request.";
+        };
+
         extraDomainNames = lib.mkOption {
           type = lib.types.listOf lib.types.str;
           default = [ ];
···
               message = ''
                 Option `security.acme.certs.${cert}.credentialFiles` can only be
                 used for variables suffixed by "_FILE".
+              '';
+            }
+
+            {
+              assertion = lib.all (
+                certOpts:
+                (certOpts.csr == null && certOpts.csrKey == null)
+                || (certOpts.csr != null && certOpts.csrKey != null)
+              ) certs;
+              message = ''
+                When passing a certificate signing request both `security.acme.certs.${cert}.csr` and `security.acme.certs.${cert}.csrKey` need to be set.
               '';
             }
           ]) cfg.certs

nixos/tests/acme/http01-builtin.nix

···
               "builtin-3.${domain}".listenHTTP = ":80";
             };
           };
+
+          csr.configuration =
+            let
+              conf = pkgs.writeText "openssl.csr.conf" ''
+                [req]
+                default_bits = 2048
+                prompt = no
+                default_md = sha256
+                req_extensions = req_ext
+                distinguished_name = dn
+
+                [ dn ]
+                CN = ${config.networking.fqdn}
+
+                [ req_ext ]
+                subjectAltName = @alt_names
+
+                [ alt_names ]
+                DNS.1 = ${config.networking.fqdn}
+              '';
+              csrData =
+                pkgs.runCommandNoCC "csr-and-key"
+                  {
+                    buildInputs = [ pkgs.openssl ];
+                  }
+                  ''
+                    mkdir -p $out
+                    openssl req -new -newkey rsa:2048 -nodes \
+                      -keyout $out/key.pem \
+                      -out $out/request.csr \
+                      -config ${conf}
+                  '';
+            in
+            {
+              security.acme.certs."${config.networking.fqdn}" = {
+                csr = "${csrData}/request.csr";
+                csrKey = "${csrData}/key.pem";
+              };
+            };
         };
       };
   };
···
 
       with subtest("Validate permissions (self-signed)"):
           check_permissions(builtin, cert, "acme")
+
+      with subtest("Can renew using a CSR"):
+          builtin.succeed(f"systemctl clean acme-{cert}.service --what=state")
+          switch_to(builtin, "csr")
+          check_issuer(builtin, cert, "pebble")
     '';
 }