diff --git a/machines/web01/metis/default.nix b/machines/web01/metis/default.nix
index 949fa6a..3f2cb14 100644
--- a/machines/web01/metis/default.nix
+++ b/machines/web01/metis/default.nix
@@ -6,30 +6,35 @@
 }:
 
 let
-  metis = import sources.metis { inherit pkgs; };
+  inherit (lib) mapAttrsToList match;
 
-  inherit (metis) providers;
+  metis = import sources.metis { inherit pkgs; };
 in
 {
   services.nginx.virtualHosts."calendrier.dgnum.eu" = {
     enableACME = true;
     forceSSL = true;
-    root = metis.production;
+    root = metis.package;
 
     locations = lib.mapAttrs' (
-      name: value:
+      name: domain:
       lib.nameValuePair "/cal/${name}/" {
         extraConfig = ''
           proxy_set_header X-Forwarded-Host $host;
           proxy_set_header X-Forwarded-Server $host;
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-          proxy_pass ${value};
+          proxy_pass https://${domain}/remote.php/dav/public-calendars/;
         '';
       }
-    ) providers;
+    ) metis.providers;
 
     extraConfig = ''
       rewrite ^/calendrier(.*)$ $1 permanent;
     '';
   };
+
+  assertions = mapAttrsToList (name: domain: {
+    assertion = (match "[a-z-]+" name == [ ]) && (match "[a-z.-]+" domain == [ ]);
+    message = "The provider `${name}` associated to the domain `${domain}` seems to have an incorrect definition.";
+  }) metis.providers;
 }
diff --git a/npins/sources.json b/npins/sources.json
index bdad599..b2feca3 100644
--- a/npins/sources.json
+++ b/npins/sources.json
@@ -178,9 +178,9 @@
         "url": "https://git.dgnum.eu/DGNum/metis"
       },
       "branch": "master",
-      "revision": "5c5e0c356bc60c15699a0830ef675af821afbb5b",
+      "revision": "ed6fafda45d638b1bafd5deaee098b80156b41e8",
       "url": null,
-      "hash": "0lijsmgcqqqrdi2qdycwsaczcjja5blvx4kx1ssclvsm8aipbbs0"
+      "hash": "086spyhn2x1x2h31b0y4an501fdhph1nk64riybqnh6mqjkzlq4m"
     },
     "microvm.nix": {
       "type": "Git",