cacerts: refactor, add blacklist option

Previously, the list of CA certificates was generated with a perl script
which is included in curl. As this script is not very flexible, this commit
refactors the expression to use the python script that Debian uses to
generate their CA certificates from Mozilla's trust store in NSS.

Additionally, an option was added to the cacerts derivation and the
`security.pki` module to blacklist specific CAs.

nixos/modules/security/ca.nix

@@ -4,10 +4,16 @@ with lib;
 
 let
 
+  cfg = config.security.pki;
+
+  cacertPackage = pkgs.cacert.override {
+    blacklist = cfg.caCertificateBlacklist;
+  };
+
   caCertificates = pkgs.runCommand "ca-certificates.crt"
     { files =
-        config.security.pki.certificateFiles ++
-        [ (builtins.toFile "extra.crt" (concatStringsSep "\n" config.security.pki.certificates)) ];
+        cfg.certificateFiles ++
+        [ (builtins.toFile "extra.crt" (concatStringsSep "\n" cfg.certificates)) ];
      }
     ''
       cat $files > $out
@@ -52,11 +58,27 @@ in
       '';
     };
 
+    security.pki.caCertificateBlacklist = mkOption {
+      type = types.listOf types.str;
+      default = [];
+      example = [
+        "WoSign" "WoSign China"
+        "CA WoSign ECC Root"
+        "Certification Authority of WoSign G2"
+      ];
+      description = ''
+        A list of blacklisted CA certificate names that won't be imported from
+        the Mozilla Trust Store into
+        <filename>/etc/ssl/certs/ca-certificates.crt</filename>. Use the
+        names from that file.
+      '';
+    };
+
   };
 
   config = {
 
-    security.pki.certificateFiles = [ "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt" ];
+    security.pki.certificateFiles = [ "${cacertPackage}/etc/ssl/certs/ca-bundle.crt" ];
 
     # NixOS canonical location + Debian/Ubuntu/Arch/Gentoo compatibility.
     environment.etc."ssl/certs/ca-certificates.crt".source = caCertificates;