diff --git a/flake.lock b/flake.lock
index ae964ea3..8c962683 100644
--- a/flake.lock
+++ b/flake.lock
@@ -234,6 +234,22 @@
         "type": "github"
       }
     },
+    "fork": {
+      "locked": {
+        "lastModified": 1729963002,
+        "narHash": "sha256-2zrYfd/qdfExU5zVwvH80uJnKc/dMeK6zp3O1UtW2Mo=",
+        "owner": "teutat3s",
+        "repo": "nixpkgs",
+        "rev": "005faaacbeede0296dec5c844f508027ab8a3ff6",
+        "type": "github"
+      },
+      "original": {
+        "owner": "teutat3s",
+        "ref": "init-matrix-authentication-service-module",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "home-manager": {
       "inputs": {
         "nixpkgs": [
@@ -354,6 +370,7 @@
         "element-stickers": "element-stickers",
         "element-themes": "element-themes",
         "flake-parts": "flake-parts",
+        "fork": "fork",
         "home-manager": "home-manager",
         "keycloak-theme-pub-solar": "keycloak-theme-pub-solar",
         "maunium-stickerpicker": "maunium-stickerpicker",
diff --git a/flake.nix b/flake.nix
index a417b498..923092cb 100644
--- a/flake.nix
+++ b/flake.nix
@@ -3,6 +3,7 @@
     # Track channels with commits tested and built by hydra
     nixpkgs.url = "github:nixos/nixpkgs/nixos-24.05";
     unstable.url = "github:nixos/nixpkgs/nixos-unstable";
+    fork.url = "github:teutat3s/nixpkgs/init-matrix-authentication-service-module";
 
     nix-darwin.url = "github:lnl7/nix-darwin/master";
     nix-darwin.inputs.nixpkgs.follows = "nixpkgs";
@@ -152,6 +153,10 @@
               hostname = "tankstelle.wg.pub.solar";
               sshUser = username;
             };
+            underground = {
+              hostname = "80.244.242.3";
+              sshUser = username;
+            };
             trinkgenossin = {
               hostname = "trinkgenossin.wg.pub.solar";
               sshUser = username;
diff --git a/hosts/default.nix b/hosts/default.nix
index 6f159d09..e7a8f2ea 100644
--- a/hosts/default.nix
+++ b/hosts/default.nix
@@ -178,6 +178,30 @@
           self.nixosModules.nginx
         ];
       };
+
+      underground = self.inputs.nixpkgs.lib.nixosSystem {
+        specialArgs = {
+          flake = {
+            inherit self inputs config;
+          };
+        };
+        modules = [
+          self.inputs.agenix.nixosModules.default
+          self.nixosModules.home-manager
+          ./underground
+          self.nixosModules.overlays
+          self.nixosModules.unlock-luks-on-boot
+          self.nixosModules.core
+
+          self.nixosModules.backups
+          self.nixosModules.keycloak
+          self.nixosModules.postgresql
+          self.nixosModules.matrix
+          self.nixosModules.matrix-irc
+          self.nixosModules.nginx
+          self.nixosModules.nginx-matrix
+        ];
+      };
     };
   };
 }
diff --git a/hosts/nachtigall/configuration.nix b/hosts/nachtigall/configuration.nix
index c226ed04..eb7e657f 100644
--- a/hosts/nachtigall/configuration.nix
+++ b/hosts/nachtigall/configuration.nix
@@ -48,6 +48,7 @@
     owner = "root";
   };
 
+  # keycloak
   age.secrets.keycloak-database-password = {
     file = "${flake.self}/secrets/keycloak-database-password.age";
     mode = "600";
@@ -59,6 +60,50 @@
     database-password-file = config.age.secrets.keycloak-database-password.path;
   };
 
+  # matrix-synapse
+  age.secrets."nachtigall-matrix-synapse-signing-key" = {
+    file = "${flake.self}/secrets/nachtigall-matrix-synapse-signing-key.age";
+    mode = "400";
+    owner = "matrix-synapse";
+  };
+
+  age.secrets."nachtigall-matrix-synapse-secret-config.yaml" = {
+    file = "${flake.self}/secrets/nachtigall-matrix-synapse-secret-config.yaml.age";
+    mode = "400";
+    owner = "matrix-synapse";
+  };
+
+  age.secrets."nachtigall-matrix-synapse-sliding-sync-secret" = {
+    file = "${flake.self}/secrets/nachtigall-matrix-synapse-sliding-sync-secret.age";
+    mode = "400";
+    owner = "matrix-synapse";
+  };
+
+
+  pub-solar-os.matrix-synapse = {
+    enable = true;
+    signing_key_path = config.age.secrets."nachtigall-matrix-synapse-signing-key".path;
+    extra-config-files = [
+      config.age.secrets."nachtigall-matrix-synapse-secret-config.yaml".path
+
+      # The registration file is automatically generated after starting the
+      # appservice for the first time.
+      # cp /var/lib/mautrix-telegram/telegram-registration.yaml \
+      #   /var/lib/matrix-synapse/
+      # chown matrix-synapse:matrix-synapse \
+      #   /var/lib/matrix-synapse/telegram-registration.yaml
+      "/var/lib/matrix-synapse/telegram-registration.yaml"
+    ];
+    app-service-config-files = [
+      "/var/lib/matrix-synapse/telegram-registration.yaml"
+      "/var/lib/matrix-appservice-irc/registration.yml"
+      # "/matrix-appservice-slack-registration.yaml"
+      # "/hookshot-registration.yml"
+      # "/matrix-mautrix-signal-registration.yaml"
+      # "/matrix-mautrix-telegram-registration.yaml"
+    ];
+  };
+
   systemd.services.postgresql = {
     after = [ "var-lib-postgresql.mount" ];
     requisite = [ "var-lib-postgresql.mount" ];
diff --git a/hosts/underground/configuration.nix b/hosts/underground/configuration.nix
new file mode 100644
index 00000000..b53f5dd6
--- /dev/null
+++ b/hosts/underground/configuration.nix
@@ -0,0 +1,107 @@
+{
+  flake,
+  config,
+  pkgs,
+  ...
+}:
+{
+  # Use GRUB2 as the boot loader.
+  boot.loader.grub = {
+    enable = true;
+    devices = [ "/dev/vda" ];
+  };
+
+  pub-solar-os.networking.domain = "test.pub.solar";
+
+  systemd.tmpfiles.rules = [ "f /tmp/dbf 1777 root root 10d password" ];
+
+  # keycloak
+  pub-solar-os.auth = {
+    enable = true;
+    database-password-file = "/tmp/dbf";
+  };
+  services.keycloak.database.createLocally = true;
+
+  # matrix-synapse
+  # test.pub.solar /.well-known is required for federation
+  services.nginx.virtualHosts."${config.pub-solar-os.networking.domain}" = {
+    default = true;
+    enableACME = true;
+    forceSSL = true;
+  };
+
+  age.secrets."underground-matrix-synapse-secret-config.yaml" = {
+    file = "${flake.self}/secrets/underground-matrix-synapse-secret-config.yaml.age";
+    mode = "400";
+    owner = "matrix-synapse";
+  };
+
+  age.secrets."underground-matrix-authentication-service-secret-config.yml" = {
+    file = "${flake.self}/secrets/underground-matrix-authentication-service-secret-config.yml.age";
+    mode = "400";
+    owner = "matrix-authentication-service";
+  };
+
+  pub-solar-os.matrix-synapse = {
+    enable = true;
+    extra-config-files = [
+      config.age.secrets."underground-matrix-synapse-secret-config.yaml".path
+
+      # The registration file is automatically generated after starting the
+      # appservice for the first time.
+      # cp /var/lib/mautrix-telegram/telegram-registration.yaml \
+      #   /var/lib/matrix-synapse/
+      # chown matrix-synapse:matrix-synapse \
+      #   /var/lib/matrix-synapse/telegram-registration.yaml
+      #"/var/lib/matrix-synapse/telegram-registration.yaml"
+    ];
+    app-service-config-files = [
+      "/var/lib/matrix-appservice-irc/registration.yml"
+      #"/var/lib/matrix-synapse/telegram-registration.yaml"
+    ];
+  };
+
+  services.matrix-authentication-service = {
+    enable = true;
+    createDatabase = true;
+    extraConfigFiles = [
+      config.age.secrets."underground-matrix-authentication-service-secret-config.yml".path
+    ];
+    settings = {
+      http.public_base = "https://mas.${config.pub-solar-os.networking.domain}";
+      http.issuer = "https://mas.${config.pub-solar-os.networking.domain}";
+      http.listeners = [
+        {
+          name = "web";
+          resources = [
+            { name = "discovery"; }
+            { name = "human"; }
+            { name = "oauth"; }
+            { name = "compat"; }
+            { name = "graphql"; }
+            { name = "assets"; path = "${config.services.matrix-authentication-service.package}/share/matrix-authentication-service/assets"; }
+          ];
+          binds = [
+            { host = "0.0.0.0"; port = 8090; }
+          ];
+          proxy_protocol = false;
+        }
+        {
+          name = "internal";
+          resources = [
+            { name = "health"; }
+          ];
+          binds = [
+            { host = "0.0.0.0"; port = 8081; }
+          ];
+          proxy_protocol = false;
+        }
+      ];
+      passwords.enabled = false;
+    };
+  };
+
+  services.openssh.openFirewall = true;
+
+  system.stateVersion = "24.05";
+}
diff --git a/hosts/underground/default.nix b/hosts/underground/default.nix
new file mode 100644
index 00000000..5a612a44
--- /dev/null
+++ b/hosts/underground/default.nix
@@ -0,0 +1,16 @@
+{ flake, ... }:
+
+{
+  imports = [
+    # Include the results of the hardware scan.
+    ./hardware-configuration.nix
+    ./configuration.nix
+
+    ./networking.nix
+    "${flake.inputs.fork}/nixos/modules/services//matrix/matrix-authentication-service.nix"
+  ];
+
+  disabledModules = [
+    "services/matrix/matrix-authentication-service.nix "
+  ];
+}
diff --git a/hosts/underground/hardware-configuration.nix b/hosts/underground/hardware-configuration.nix
new file mode 100644
index 00000000..e4738a1b
--- /dev/null
+++ b/hosts/underground/hardware-configuration.nix
@@ -0,0 +1,34 @@
+# Do not modify this file!  It was generated by ‘nixos-generate-config’
+# and may be overwritten by future invocations.  Please make changes
+# to /etc/nixos/configuration.nix instead.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports =
+    [ (modulesPath + "/profiles/qemu-guest.nix")
+    ];
+
+  boot.initrd.availableKernelModules = [ "ahci" "xhci_pci" "virtio_pci" "virtio_scsi" "sd_mod" "sr_mod" ];
+  boot.kernelModules = [ "kvm-intel" ];
+  boot.extraModulePackages = [ ];
+
+  boot.initrd.luks.devices."cryptroot" = {
+    device = "/dev/disk/by-label/cryptroot";
+  };
+
+  fileSystems."/" =
+    { device = "/dev/disk/by-label/root";
+      fsType = "ext4";
+    };
+
+  fileSystems."/boot" =
+    { device = "/dev/disk/by-label/boot";
+      fsType = "ext4";
+    };
+
+  swapDevices =
+    [ { device = "/dev/disk/by-label/swap"; }
+    ];
+
+  nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
+}
diff --git a/hosts/underground/networking.nix b/hosts/underground/networking.nix
new file mode 100644
index 00000000..3085c7bc
--- /dev/null
+++ b/hosts/underground/networking.nix
@@ -0,0 +1,24 @@
+{
+  config,
+  pkgs,
+  flake,
+  ...
+}:
+{
+
+  networking.hostName = "underground";
+
+  networking = {
+    defaultGateway = {
+      address = "80.244.242.1";
+      interface = "enp1s0";
+    };
+    nameservers = ["95.129.51.51" "80.244.244.244"];
+    interfaces.enp1s0 = {
+      useDHCP = false;
+      ipv4.addresses = [
+        { address = "80.244.242.3"; prefixLength = 29; }
+      ];
+    };
+  };
+}
diff --git a/modules/coturn/default.nix b/modules/coturn/default.nix
index d8635aab..a7d3e867 100644
--- a/modules/coturn/default.nix
+++ b/modules/coturn/default.nix
@@ -5,8 +5,8 @@
   ...
 }:
 {
-  age.secrets."coturn-static-auth-secret" = {
-    file = "${flake.self}/secrets/coturn-static-auth-secret.age";
+  age.secrets."nachtigall-coturn-static-auth-secret" = {
+    file = "${flake.self}/secrets/nachtigall-coturn-static-auth-secret.age";
     mode = "400";
     owner = "turnserver";
   };
@@ -18,7 +18,7 @@
     min-port = 49000;
     max-port = 50000;
     use-auth-secret = true;
-    static-auth-secret-file = "/run/agenix/coturn-static-auth-secret";
+    static-auth-secret-file = "/run/agenix/nachtigall-coturn-static-auth-secret";
     realm = "turn.${config.pub-solar-os.networking.domain}";
     cert = "${config.security.acme.certs.${realm}.directory}/full.pem";
     pkey = "${config.security.acme.certs.${realm}.directory}/key.pem";
diff --git a/modules/matrix-irc/default.nix b/modules/matrix-irc/default.nix
index f64d25c1..02217d29 100644
--- a/modules/matrix-irc/default.nix
+++ b/modules/matrix-irc/default.nix
@@ -16,11 +16,6 @@ let
   synapseClientPort = "${toString listenerWithClient.port}";
 in
 {
-  systemd.services.matrix-appservice-irc.serviceConfig.SystemCallFilter = lib.mkForce [
-    "@system-service @pkey"
-    "~@privileged @resources"
-    "@chown"
-  ];
   services.matrix-appservice-irc = {
     enable = true;
     localpart = "irc_bot";
diff --git a/modules/matrix/default.nix b/modules/matrix/default.nix
index 3165911c..d8518d3f 100644
--- a/modules/matrix/default.nix
+++ b/modules/matrix/default.nix
@@ -1,6 +1,7 @@
 {
   flake,
   config,
+  lib,
   pkgs,
   ...
 }:
@@ -9,304 +10,291 @@ let
   serverDomain = "${config.pub-solar-os.networking.domain}";
 in
 {
-  age.secrets."matrix-synapse-signing-key" = {
-    file = "${flake.self}/secrets/matrix-synapse-signing-key.age";
-    mode = "400";
-    owner = "matrix-synapse";
+  options.pub-solar-os.matrix-synapse = {
+    enable = lib.mkEnableOption "Enable matrix-synapse to run on the node";
+
+    app-service-config-files = lib.mkOption {
+      description = "List of app service config files";
+      type = lib.types.listOf lib.types.str;
+      default = [];
+    };
+
+    extra-config-files = lib.mkOption {
+      description = "List of extra synapse config files";
+      type = lib.types.listOf lib.types.str;
+      default = [];
+    };
+
+    signing_key_path = lib.mkOption {
+      description = "Path to file containing the signing key";
+      type = lib.types.str;
+      default = "${config.services.matrix-synapse.dataDir}/homeserver.signing.key";
+    };
   };
 
-  age.secrets."matrix-synapse-secret-config.yaml" = {
-    file = "${flake.self}/secrets/matrix-synapse-secret-config.yaml.age";
-    mode = "400";
-    owner = "matrix-synapse";
-  };
-
-  age.secrets."matrix-synapse-sliding-sync-secret" = {
-    file = "${flake.self}/secrets/matrix-synapse-sliding-sync-secret.age";
-    mode = "400";
-    owner = "matrix-synapse";
-  };
-
-  services.matrix-synapse = {
-    enable = true;
-    settings = {
-      server_name = serverDomain;
-      public_baseurl = "https://${publicDomain}/";
-      database = {
-        name = "psycopg2";
-        args = {
-          host = "/run/postgresql";
-          cp_max = 10;
-          cp_min = 5;
-          database = "matrix";
+  config = lib.mkIf config.pub-solar-os.matrix-synapse.enable {
+    services.matrix-synapse = {
+      enable = true;
+      settings = {
+        server_name = serverDomain;
+        public_baseurl = "https://${publicDomain}/";
+        database = {
+          name = "psycopg2";
+          args = {
+            host = "/run/postgresql";
+            cp_max = 10;
+            cp_min = 5;
+            database = "matrix";
+          };
+          allow_unsafe_locale = false;
+          txn_limit = 0;
         };
-        allow_unsafe_locale = false;
-        txn_limit = 0;
-      };
-      listeners = [
-        {
-          bind_addresses = [ "127.0.0.1" ];
-          port = 8008;
-          resources = [
-            {
-              compress = true;
-              names = [ "client" ];
-            }
-            {
-              compress = false;
-              names = [ "federation" ];
-            }
-          ];
-          tls = false;
-          type = "http";
-          x_forwarded = true;
-        }
-        {
-          bind_addresses = [ "127.0.0.1" ];
-          port = 8012;
-          resources = [ { names = [ "metrics" ]; } ];
-          tls = false;
-          type = "metrics";
-        }
-      ];
+        listeners = [
+          {
+            bind_addresses = [ "127.0.0.1" ];
+            port = 8008;
+            resources = [
+              {
+                compress = true;
+                names = [ "client" ];
+              }
+              {
+                compress = false;
+                names = [ "federation" ];
+              }
+            ];
+            tls = false;
+            type = "http";
+            x_forwarded = true;
+          }
+          {
+            bind_addresses = [ "127.0.0.1" ];
+            port = 8012;
+            resources = [ { names = [ "metrics" ]; } ];
+            tls = false;
+            type = "metrics";
+          }
+        ];
 
-      account_threepid_delegates.msisdn = "";
-      alias_creation_rules = [
-        {
-          action = "allow";
-          alias = "*";
-          room_id = "*";
-          user_id = "*";
-        }
-      ];
-      allow_guest_access = false;
-      allow_public_rooms_over_federation = true;
-      allow_public_rooms_without_auth = false;
-      auto_join_rooms = [
-        "#community:${serverDomain}"
-        "#general:${serverDomain}"
-      ];
+        account_threepid_delegates.msisdn = "";
+        alias_creation_rules = [
+          {
+            action = "allow";
+            alias = "*";
+            room_id = "*";
+            user_id = "*";
+          }
+        ];
+        allow_guest_access = false;
+        allow_public_rooms_over_federation = true;
+        allow_public_rooms_without_auth = false;
+        auto_join_rooms = [
+          "#community:${serverDomain}"
+          "#general:${serverDomain}"
+        ];
 
-      autocreate_auto_join_rooms = true;
-      caches.global_factor = 0.5;
+        autocreate_auto_join_rooms = true;
+        caches.global_factor = 0.5;
 
-      default_room_version = "10";
-      disable_msisdn_registration = true;
-      enable_media_repo = true;
-      enable_metrics = true;
-      mau_stats_only = true;
-      enable_registration = false;
-      enable_registration_captcha = false;
-      enable_registration_without_verification = false;
-      enable_room_list_search = true;
-      encryption_enabled_by_default_for_room_type = "off";
-      event_cache_size = "100K";
-      federation_rr_transactions_per_room_per_second = 50;
-      federation_client_minimum_tls_version = "1.2";
-      forget_rooms_on_leave = true;
-      include_profile_data_on_invite = true;
-      instance_map = { };
-      limit_profile_requests_to_users_who_share_rooms = false;
+        default_room_version = "10";
+        disable_msisdn_registration = true;
+        enable_media_repo = true;
+        enable_metrics = true;
+        mau_stats_only = true;
+        enable_registration = false;
+        enable_registration_captcha = false;
+        enable_registration_without_verification = false;
+        enable_room_list_search = true;
+        encryption_enabled_by_default_for_room_type = "off";
+        event_cache_size = "100K";
+        federation_rr_transactions_per_room_per_second = 50;
+        federation_client_minimum_tls_version = "1.2";
+        forget_rooms_on_leave = true;
+        include_profile_data_on_invite = true;
+        instance_map = { };
+        limit_profile_requests_to_users_who_share_rooms = false;
 
-      max_spider_size = "10M";
-      max_upload_size = "50M";
-      media_storage_providers = [ ];
+        max_spider_size = "10M";
+        max_upload_size = "50M";
+        media_storage_providers = [ ];
 
-      password_config = {
-        enabled = false;
-        localdb_enabled = false;
-        pepper = "";
-      };
+        password_config = {
+          enabled = false;
+          localdb_enabled = false;
+          pepper = "";
+        };
 
-      presence.enabled = true;
-      push.include_content = false;
+        presence.enabled = true;
+        push.include_content = false;
 
-      rc_admin_redaction = {
-        burst_count = 50;
-        per_second = 1;
-      };
-      rc_federation = {
-        concurrent = 3;
-        reject_limit = 50;
-        sleep_delay = 500;
-        sleep_limit = 10;
-        window_size = 1000;
-      };
-      rc_invites = {
-        per_issuer = {
+        rc_admin_redaction = {
+          burst_count = 50;
+          per_second = 1;
+        };
+        rc_federation = {
+          concurrent = 3;
+          reject_limit = 50;
+          sleep_delay = 500;
+          sleep_limit = 10;
+          window_size = 1000;
+        };
+        rc_invites = {
+          per_issuer = {
+            burst_count = 10;
+            per_second = 0.3;
+          };
+          per_room = {
+            burst_count = 10;
+            per_second = 0.3;
+          };
+          per_user = {
+            burst_count = 5;
+            per_second = 3.0e-3;
+          };
+        };
+        rc_joins = {
+          local = {
+            burst_count = 10;
+            per_second = 0.1;
+          };
+          remote = {
+            burst_count = 10;
+            per_second = 1.0e-2;
+          };
+        };
+        rc_login = {
+          account = {
+            burst_count = 3;
+            per_second = 0.17;
+          };
+          address = {
+            burst_count = 3;
+            per_second = 0.17;
+          };
+          failed_attempts = {
+            burst_count = 3;
+            per_second = 0.17;
+          };
+        };
+        rc_message = {
           burst_count = 10;
-          per_second = 0.3;
+          per_second = 0.2;
         };
-        per_room = {
-          burst_count = 10;
-          per_second = 0.3;
-        };
-        per_user = {
-          burst_count = 5;
-          per_second = 3.0e-3;
-        };
-      };
-      rc_joins = {
-        local = {
-          burst_count = 10;
-          per_second = 0.1;
-        };
-        remote = {
-          burst_count = 10;
-          per_second = 1.0e-2;
-        };
-      };
-      rc_login = {
-        account = {
+        rc_registration = {
           burst_count = 3;
           per_second = 0.17;
         };
-        address = {
-          burst_count = 3;
-          per_second = 0.17;
-        };
-        failed_attempts = {
-          burst_count = 3;
-          per_second = 0.17;
+        redaction_retention_period = "7d";
+        forgotten_room_retention_period = "7d";
+        redis.enabled = false;
+        registration_requires_token = false;
+        registrations_require_3pid = [ "email" ];
+        report_stats = false;
+        require_auth_for_profile_requests = false;
+        room_list_publication_rules = [
+          {
+            action = "allow";
+            alias = "*";
+            room_id = "*";
+            user_id = "*";
+          }
+        ];
+
+        signing_key_path = config.pub-solar-os.matrix-synapse.signing_key_path;
+
+        stream_writers = { };
+        trusted_key_servers = [ { server_name = "matrix.org"; } ];
+        suppress_key_server_warning = true;
+
+        turn_allow_guests = false;
+        turn_uris = [
+          "turn:${config.services.coturn.realm}:3478?transport=udp"
+          "turn:${config.services.coturn.realm}:3478?transport=tcp"
+        ];
+        turn_user_lifetime = "1h";
+
+        url_preview_accept_language = [
+          "en-US"
+          "en"
+        ];
+        url_preview_enabled = true;
+        url_preview_ip_range_blacklist = [
+          "127.0.0.0/8"
+          "10.0.0.0/8"
+          "172.16.0.0/12"
+          "192.168.0.0/16"
+          "100.64.0.0/10"
+          "192.0.0.0/24"
+          "169.254.0.0/16"
+          "192.88.99.0/24"
+          "198.18.0.0/15"
+          "192.0.2.0/24"
+          "198.51.100.0/24"
+          "203.0.113.0/24"
+          "224.0.0.0/4"
+          "::1/128"
+          "fe80::/10"
+          "fc00::/7"
+          "2001:db8::/32"
+          "ff00::/8"
+          "fec0::/10"
+        ];
+
+        user_directory = {
+          prefer_local_users = false;
+          search_all_users = false;
         };
+        user_ips_max_age = "28d";
+
+        app_service_config_files = config.pub-solar-os.matrix-synapse.app-service-config-files;
       };
-      rc_message = {
-        burst_count = 10;
-        per_second = 0.2;
-      };
-      rc_registration = {
-        burst_count = 3;
-        per_second = 0.17;
-      };
-      redaction_retention_period = "7d";
-      forgotten_room_retention_period = "7d";
-      redis.enabled = false;
-      registration_requires_token = false;
-      registrations_require_3pid = [ "email" ];
-      report_stats = false;
-      require_auth_for_profile_requests = false;
-      room_list_publication_rules = [
-        {
-          action = "allow";
-          alias = "*";
-          room_id = "*";
-          user_id = "*";
-        }
+
+      withJemalloc = true;
+
+      extraConfigFiles = config.pub-solar-os.matrix-synapse.extra-config-files;
+
+      extras = [
+        "oidc"
+        "redis"
       ];
 
-      signing_key_path = "/run/agenix/matrix-synapse-signing-key";
-
-      stream_writers = { };
-      trusted_key_servers = [ { server_name = "matrix.org"; } ];
-      suppress_key_server_warning = true;
-
-      turn_allow_guests = false;
-      turn_uris = [
-        "turn:${config.services.coturn.realm}:3478?transport=udp"
-        "turn:${config.services.coturn.realm}:3478?transport=tcp"
-      ];
-      turn_user_lifetime = "1h";
-
-      url_preview_accept_language = [
-        "en-US"
-        "en"
-      ];
-      url_preview_enabled = true;
-      url_preview_ip_range_blacklist = [
-        "127.0.0.0/8"
-        "10.0.0.0/8"
-        "172.16.0.0/12"
-        "192.168.0.0/16"
-        "100.64.0.0/10"
-        "192.0.0.0/24"
-        "169.254.0.0/16"
-        "192.88.99.0/24"
-        "198.18.0.0/15"
-        "192.0.2.0/24"
-        "198.51.100.0/24"
-        "203.0.113.0/24"
-        "224.0.0.0/4"
-        "::1/128"
-        "fe80::/10"
-        "fc00::/7"
-        "2001:db8::/32"
-        "ff00::/8"
-        "fec0::/10"
-      ];
-
-      user_directory = {
-        prefer_local_users = false;
-        search_all_users = false;
-      };
-      user_ips_max_age = "28d";
-
-      app_service_config_files = [
-        "/var/lib/matrix-synapse/telegram-registration.yaml"
-        "/var/lib/matrix-appservice-irc/registration.yml"
-        # "/matrix-appservice-slack-registration.yaml"
-        # "/hookshot-registration.yml"
-        # "/matrix-mautrix-signal-registration.yaml"
-        # "/matrix-mautrix-telegram-registration.yaml"
-      ];
+      plugins = [ config.services.matrix-synapse.package.plugins.matrix-synapse-shared-secret-auth ];
     };
 
-    withJemalloc = true;
+    #services.matrix-sliding-sync = {
+    #  enable = true;
+    #  settings = {
+    #    SYNCV3_SERVER = "https://${publicDomain}";
+    #    SYNCV3_BINDADDR = "127.0.0.1:8011";
+    #    # The bind addr for Prometheus metrics, which will be accessible at
+    #    # /metrics at this address
+    #    SYNCV3_PROM = "127.0.0.1:9100";
+    #  };
+    #  environmentFile = config.age.secrets."matrix-synapse-sliding-sync-secret".path;
+    #};
 
-    extraConfigFiles = [
-      "/run/agenix/matrix-synapse-secret-config.yaml"
-
-      # The registration file is automatically generated after starting the
-      # appservice for the first time.
-      # cp /var/lib/mautrix-telegram/telegram-registration.yaml \
-      #   /var/lib/matrix-synapse/
-      # chown matrix-synapse:matrix-synapse \
-      #   /var/lib/matrix-synapse/telegram-registration.yaml
-      "/var/lib/matrix-synapse/telegram-registration.yaml"
-    ];
-
-    extras = [
-      "oidc"
-      "redis"
-    ];
-
-    plugins = [ config.services.matrix-synapse.package.plugins.matrix-synapse-shared-secret-auth ];
-  };
-
-  services.matrix-sliding-sync = {
-    enable = true;
-    settings = {
-      SYNCV3_SERVER = "https://${publicDomain}";
-      SYNCV3_BINDADDR = "127.0.0.1:8011";
-      # The bind addr for Prometheus metrics, which will be accessible at
-      # /metrics at this address
-      SYNCV3_PROM = "127.0.0.1:9100";
+    pub-solar-os.backups.restic.matrix-synapse = {
+      paths = [
+        "/var/lib/matrix-synapse"
+        "/var/lib/matrix-appservice-irc"
+        "/var/lib/mautrix-telegram"
+        "/tmp/matrix-synapse-backup.sql"
+      ];
+      timerConfig = {
+        OnCalendar = "*-*-* 05:00:00 Etc/UTC";
+      };
+      initialize = true;
+      backupPrepareCommand = ''
+        ${pkgs.sudo}/bin/sudo -u postgres ${pkgs.postgresql}/bin/pg_dump -d matrix > /tmp/matrix-synapse-backup.sql
+      '';
+      backupCleanupCommand = ''
+        rm /tmp/matrix-synapse-backup.sql
+      '';
+      pruneOpts = [
+        "--keep-daily 7"
+        "--keep-weekly 4"
+        "--keep-monthly 3"
+      ];
     };
-    environmentFile = config.age.secrets."matrix-synapse-sliding-sync-secret".path;
-  };
-
-  services.restic.backups.matrix-synapse-storagebox = {
-    paths = [
-      "/var/lib/matrix-synapse"
-      "/var/lib/matrix-appservice-irc"
-      "/var/lib/mautrix-telegram"
-      "/tmp/matrix-synapse-backup.sql"
-    ];
-    timerConfig = {
-      OnCalendar = "*-*-* 05:00:00 Etc/UTC";
-    };
-    initialize = true;
-    passwordFile = config.age.secrets."restic-repo-storagebox-nachtigall".path;
-    repository = "sftp:u377325@u377325.your-storagebox.de:/backups";
-    backupPrepareCommand = ''
-      ${pkgs.sudo}/bin/sudo -u postgres ${pkgs.postgresql}/bin/pg_dump -d matrix > /tmp/matrix-synapse-backup.sql
-    '';
-    backupCleanupCommand = ''
-      rm /tmp/matrix-synapse-backup.sql
-    '';
-    pruneOpts = [
-      "--keep-daily 7"
-      "--keep-weekly 4"
-      "--keep-monthly 3"
-    ];
   };
 }
diff --git a/modules/nginx-matrix/default.nix b/modules/nginx-matrix/default.nix
index 0e236dce..603de360 100644
--- a/modules/nginx-matrix/default.nix
+++ b/modules/nginx-matrix/default.nix
@@ -10,11 +10,14 @@ let
     add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
     add_header X-XSS-Protection "1; mode=block";
   '';
-  clientConfig = import ./element-client-config.nix { inherit lib pkgs; };
+  clientConfig = import ./element-client-config.nix { inherit config lib pkgs; };
   wellKnownClient = domain: {
     "m.homeserver".base_url = "https://matrix.${domain}";
     "m.identity_server".base_url = "https://matrix.${domain}";
-    "org.matrix.msc3575.proxy".url = "https://matrix.${domain}";
+    "org.matrix.msc2965.authentication" = {
+      issuer = "https://mas.${domain}/";
+      account = "https://mas.${domain}/account";
+    };
     "im.vector.riot.e2ee".default = true;
     "io.element.e2ee" = {
       default = true;
@@ -85,6 +88,27 @@ in
       root = pkgs.element-stickerpicker;
     };
 
+    "mas.${config.pub-solar-os.networking.domain}" = {
+      root = "/dev/null";
+
+      forceSSL = lib.mkDefault true;
+      enableACME = lib.mkDefault true;
+
+      locations = {
+        "/" = {
+          proxyPass = "http://127.0.0.1:8090";
+
+          extraConfig = ''
+            ${commonHeaders}
+            proxy_http_version 1.1;
+
+            # Forward the client IP address
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+          '';
+        };
+      };
+    };
+
     "matrix.${config.pub-solar-os.networking.domain}" = {
       root = "/dev/null";
 
@@ -99,28 +123,41 @@ in
       locations = {
         # For telegram
         "/c3c3f34b-29fb-5feb-86e5-98c75ec8214b" = {
+          priority = 100;
           proxyPass = "http://127.0.0.1:8009";
           extraConfig = commonHeaders;
         };
 
-        # sliding-sync
-        "~ ^/(client/|_matrix/client/unstable/org.matrix.msc3575/sync)" = {
-          proxyPass = "http://127.0.0.1:8011";
-          extraConfig = commonHeaders;
+        # Forward to the auth service
+        "~ ^/_matrix/client/(.*)/(login|logout|refresh)" = {
+          priority = 100;
+          proxyPass = "http://127.0.0.1:8090";
+
+          extraConfig = ''
+            ${commonHeaders}
+            proxy_http_version 1.1;
+
+            # Forward the client IP address
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+          '';
         };
 
-        "~* ^(/_matrix|/_synapse/client|/_synapse/oidc)" = {
+        # Forward to Synapse
+        # as per https://element-hq.github.io/synapse/latest/reverse_proxy.html#nginx
+        "~ ^(/_matrix|/_synapse/client)" = {
+          priority = 200;
           proxyPass = "http://127.0.0.1:8008";
 
           extraConfig = ''
             ${commonHeaders}
+            proxy_set_header X-Forwarded-For $remote_addr;
+            proxy_set_header X-Forwarded-Proto $scheme;
             proxy_set_header Host $host;
-            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $http_x_forwarded_proto;
 
             client_body_buffer_size 25M;
             client_max_body_size 50M;
             proxy_max_temp_file_size 0;
+            proxy_http_version 1.1;
           '';
         };
       };
diff --git a/modules/nginx-matrix/element-client-config.nix b/modules/nginx-matrix/element-client-config.nix
index b3eaf9b1..617d3bc3 100644
--- a/modules/nginx-matrix/element-client-config.nix
+++ b/modules/nginx-matrix/element-client-config.nix
@@ -1,9 +1,9 @@
-{ pkgs, lib, ... }:
+{ config, pkgs, lib, ... }:
 {
   default_server_config = {
     "m.homeserver" = {
-      base_url = "https://matrix.pub.solar";
-      server_name = "pub.solar";
+      base_url = "https://matrix.${config.pub-solar-os.networking.domain}";
+      server_name = "${config.pub-solar-os.networking.domain}";
     };
     "m.identity_server" = {
       base_url = "";
diff --git a/overlays/default.nix b/overlays/default.nix
index 50ede5d3..33f0e1de 100644
--- a/overlays/default.nix
+++ b/overlays/default.nix
@@ -17,6 +17,7 @@
                   inherit (inputs) element-stickers maunium-stickerpicker;
                 };
                 mastodon = unstable.mastodon;
+                matrix-authentication-service = unstable.matrix-authentication-service;
               }
             )
           ];
diff --git a/secrets/coturn-static-auth-secret.age b/secrets/nachtigall-coturn-static-auth-secret.age
similarity index 100%
rename from secrets/coturn-static-auth-secret.age
rename to secrets/nachtigall-coturn-static-auth-secret.age
diff --git a/secrets/matrix-synapse-secret-config.yaml.age b/secrets/nachtigall-matrix-synapse-secret-config.yaml.age
similarity index 100%
rename from secrets/matrix-synapse-secret-config.yaml.age
rename to secrets/nachtigall-matrix-synapse-secret-config.yaml.age
diff --git a/secrets/matrix-synapse-signing-key.age b/secrets/nachtigall-matrix-synapse-signing-key.age
similarity index 100%
rename from secrets/matrix-synapse-signing-key.age
rename to secrets/nachtigall-matrix-synapse-signing-key.age
diff --git a/secrets/matrix-synapse-sliding-sync-secret.age b/secrets/nachtigall-matrix-synapse-sliding-sync-secret.age
similarity index 100%
rename from secrets/matrix-synapse-sliding-sync-secret.age
rename to secrets/nachtigall-matrix-synapse-sliding-sync-secret.age
diff --git a/secrets/secrets.nix b/secrets/secrets.nix
index 999cec92..402fc79d 100644
--- a/secrets/secrets.nix
+++ b/secrets/secrets.nix
@@ -7,6 +7,7 @@ let
   trinkgenossin-host = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIDZXRDpom/LtyoCxvRuoONARKxIT6wNUwEyUjzHRE7DG root@trinkgenossin";
   delite-host = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAKo7zlfQhcJ5/okFTOoOstZtmEL1iNlHxQ4q2baEcWT root@delite";
   blue-shell-host = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIP9g9X0a/MaVtbh44IeLxcq+McuYec0GYAdLsseBpk5f root@blue-shell";
+  underground-host = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGF3PtA89yhVkmN7aJI6gqXK8DW9L7kI71IgiK4TAEwI root@underground";
 
   adminKeys = builtins.foldl' (
     keys: login: keys ++ (builtins.attrValues login.secretEncryptionKeys)
@@ -24,6 +25,8 @@ let
 
   blueshellKeys = [ blue-shell-host ];
 
+  undergroundKeys = [ underground-host ];
+
   garageKeys = [
     trinkgenossin-host
     delite-host
@@ -62,9 +65,12 @@ in
   "forgejo-ssh-private-key.age".publicKeys = nachtigallKeys ++ adminKeys;
 
   "matrix-mautrix-telegram-env-file.age".publicKeys = nachtigallKeys ++ adminKeys;
-  "matrix-synapse-signing-key.age".publicKeys = nachtigallKeys ++ adminKeys;
-  "matrix-synapse-secret-config.yaml.age".publicKeys = nachtigallKeys ++ adminKeys;
-  "matrix-synapse-sliding-sync-secret.age".publicKeys = nachtigallKeys ++ adminKeys;
+  "nachtigall-matrix-synapse-signing-key.age".publicKeys = nachtigallKeys ++ adminKeys;
+  "nachtigall-matrix-synapse-secret-config.yaml.age".publicKeys = nachtigallKeys ++ adminKeys;
+  "nachtigall-matrix-synapse-sliding-sync-secret.age".publicKeys = nachtigallKeys ++ adminKeys;
+
+  "underground-matrix-synapse-secret-config.yaml.age".publicKeys = undergroundKeys ++ adminKeys;
+  "underground-matrix-authentication-service-secret-config.yml.age".publicKeys = undergroundKeys ++ adminKeys;
 
   "nextcloud-secrets.age".publicKeys = nachtigallKeys ++ adminKeys;
   "nextcloud-admin-pass.age".publicKeys = nachtigallKeys ++ adminKeys;
@@ -84,7 +90,7 @@ in
   "mediawiki-oidc-client-secret.age".publicKeys = nachtigallKeys ++ adminKeys;
   "mediawiki-secret-key.age".publicKeys = nachtigallKeys ++ adminKeys;
 
-  "coturn-static-auth-secret.age".publicKeys = nachtigallKeys ++ adminKeys;
+  "nachtigall-coturn-static-auth-secret.age".publicKeys = nachtigallKeys ++ adminKeys;
 
   "grafana-admin-password.age".publicKeys = trinkgenossinKeys ++ adminKeys;
   "grafana-keycloak-client-secret.age".publicKeys = trinkgenossinKeys ++ adminKeys;
diff --git a/secrets/underground-matrix-authentication-service-secret-config.yml.age b/secrets/underground-matrix-authentication-service-secret-config.yml.age
new file mode 100644
index 00000000..eaab469c
Binary files /dev/null and b/secrets/underground-matrix-authentication-service-secret-config.yml.age differ
diff --git a/secrets/underground-matrix-synapse-secret-config.yaml.age b/secrets/underground-matrix-synapse-secret-config.yaml.age
new file mode 100644
index 00000000..54154b9e
Binary files /dev/null and b/secrets/underground-matrix-synapse-secret-config.yaml.age differ
diff --git a/terraform/dns.tf b/terraform/dns.tf
index d4a8d431..5372c390 100644
--- a/terraform/dns.tf
+++ b/terraform/dns.tf
@@ -332,10 +332,40 @@ resource "namecheap_domain_records" "pub-solar" {
     type     = "AAAA"
     address  = "2a01:4f8:172:1c25::1"
   }
+  record {
+    hostname = "underground"
+    type     = "A"
+    address  = "80.244.242.3"
+  }
+  record {
+    hostname = "test"
+    type     = "CNAME"
+    address  = "underground.pub.solar."
+  }
+  record {
+    hostname = "mas.test"
+    type     = "CNAME"
+    address  = "underground.pub.solar."
+  }
   record {
     hostname = "matrix.test"
     type     = "CNAME"
-    address  = "nachtigall.pub.solar."
+    address  = "underground.pub.solar."
+  }
+  record {
+    hostname = "chat.test"
+    type     = "CNAME"
+    address  = "underground.pub.solar."
+  }
+  record {
+    hostname = "stickers.chat.test"
+    type     = "CNAME"
+    address  = "underground.pub.solar."
+  }
+  record {
+    hostname = "auth.test"
+    type     = "CNAME"
+    address  = "underground.pub.solar."
   }
   # SRV records can only be changed via NameCheap Web UI
   # add comment