From fd898df5903e459982426a61a6e1b4d8e989baa3 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 30 Aug 2021 14:53:13 +0200
Subject: [PATCH] modules: services: nginx: add SSO

---
 modules/services/nginx.nix | 125 +++++++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/modules/services/nginx.nix b/modules/services/nginx.nix
index c2c3a4d..f78c2df 100644
--- a/modules/services/nginx.nix
+++ b/modules/services/nginx.nix
@@ -34,6 +34,10 @@ let
         '';
       };
 
+      sso = {
+        enable = mkEnableOption "SSO authentication";
+      };
+
       extraConfig = mkOption {
         type = types.attrs; # FIXME: forward type of virtualHosts
         example = litteralExample ''
@@ -89,6 +93,22 @@ in
         List of virtual hosts to set-up using default settings.
       '';
     };
+
+    sso = {
+      subdomain = mkOption {
+        type = types.str;
+        default = "login";
+        example = "auth";
+        description = "Which subdomain, to use for SSO.";
+      };
+
+      port = mkOption {
+        type = types.port;
+        default = 8082;
+        example = 8080;
+        description = "Port to use for internal webui.";
+      };
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -170,12 +190,117 @@ in
               })
               # VHost specific configuration
               args.extraConfig
+              # SSO configuration
+              (lib.optionalAttrs args.sso.enable {
+                extraConfig = (args.extraConfig.extraConfig or "") + ''
+                  error_page 401 = @error401;
+                '';
+
+                locations."@error401".return = ''
+                  302 https://${cfg.sso.subdomain}.${config.networking.domain}/login?go=$scheme://$http_host$request_uri
+                '';
+
+                locations."/" = {
+                  extraConfig =
+                    (args.extraConfig.locations."/".extraConfig or "") + ''
+                      # Use SSO
+                      auth_request /sso-auth;
+
+                      # Set username through header
+                      auth_request_set $username $upstream_http_x_username;
+                      proxy_set_header X-User $username;
+
+                      # Renew SSO cookie on request
+                      auth_request_set $cookie $upstream_http_set_cookie;
+                      add_header Set-Cookie $cookie;
+                    '';
+                };
+
+                locations."/sso-auth" = {
+                  proxyPass = "http://localhost:${toString cfg.sso.port}/auth";
+                  extraConfig = ''
+                    # Do not allow requests from outside
+                    internal;
+
+                    # Do not forward the request body
+                    proxy_pass_request_body off;
+                    proxy_set_header Content-Length "";
+
+                    # Set X-Application according to subdomain for matching
+                    proxy_set_header X-Application "${subdomain}";
+
+                    # Set origin URI for matching
+                    proxy_set_header X-Origin-URI $request_uri;
+                  '';
+                };
+              })
             ])
           );
         in
         lib.my.genAttrs' cfg.virtualHosts mkVHost;
+
+      sso = {
+        enable = true;
+
+        configuration = {
+          listen = {
+            addr = "127.0.0.1";
+            inherit (cfg.sso) port;
+          };
+
+          cookie = {
+            domain = ".${config.networking.domain}";
+            secure = true;
+            authentication_key = config.my.secrets.sso.auth_key;
+          };
+
+          login = {
+            title = "Ambroisie's SSO";
+            default_method = "simple";
+            hide_mfa_field = false;
+            names = {
+              simple = "Username / Password";
+            };
+          };
+
+          providers = {
+            simple =
+              let
+                applyUsers = lib.flip lib.mapAttrs config.my.secrets.sso.users;
+              in
+              {
+                users = applyUsers (_: v: v.passwordHash);
+
+                mfa = applyUsers (_: v: [{
+                  provider = "totp";
+                  attributes = {
+                    secret = v.totpSecret;
+                  };
+                }]);
+
+                inherit (config.my.secrets.sso) groups;
+              };
+          };
+
+          acl = {
+            rule_sets = [
+              {
+                rules = [{ field = "x-application"; present = true; }];
+                allow = [ "@root" ];
+              }
+            ];
+          };
+        };
+      };
     };
 
+    my.services.nginx.virtualHosts = [
+      {
+        subdomain = "login";
+        inherit (cfg.sso) port;
+      }
+    ];
+
     networking.firewall.allowedTCPPorts = [ 80 443 ];
 
     # Nginx needs to be able to read the certificates