nixos/acme: add ocspMustStaple option

nixos/modules/security/acme.nix

@@ -136,6 +136,19 @@ let
           challenge to ensure the DNS entries required are available.
         '';
       };
+
+      ocspMustStaple = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Turns on the OCSP Must-Staple TLS extension.
+          Make sure you know what you're doing! See:
+          <itemizedlist>
+            <listitem><para><link xlink:href="https://blog.apnic.net/2019/01/15/is-the-web-ready-for-ocsp-must-staple/" /></para></listitem>
+            <listitem><para><link xlink:href="https://blog.hboeck.de/archives/886-The-Problem-with-OCSP-Stapling-and-Must-Staple-and-why-Certificate-Revocation-is-still-broken.html" /></para></listitem>
+          </itemizedlist>
+        '';
+      };
     };
   };
 
@@ -288,8 +301,11 @@ in
                           ++ concatLists (mapAttrsToList (name: root: [ "-d" name ]) data.extraDomains)
                           ++ (if data.dnsProvider != null then [ "--dns" data.dnsProvider ] else [ "--http" "--http.webroot" data.webroot ])
                           ++ optionals (cfg.server != null || data.server != null) ["--server" (if data.server == null then cfg.server else data.server)];
-                runOpts = escapeShellArgs (globalOpts ++ [ "run" ]);
-                renewOpts = escapeShellArgs (globalOpts ++ [ "renew" "--days" (toString cfg.validMinDays) ]);
+                certOpts = optionals data.ocspMustStaple [ "--must-staple" ];
+                runOpts = escapeShellArgs (globalOpts ++ [ "run" ] ++ certOpts);
+                renewOpts = escapeShellArgs (globalOpts ++
+                  [ "renew" "--days" (toString cfg.validMinDays) ] ++
+                  certOpts);
                 acmeService = {
                   description = "Renew ACME Certificate for ${cert}";
                   after = [ "network.target" "network-online.target" ];