diff --git a/README.md b/README.md
index 38486c6..7cd076b 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,7 @@ Currently it is in a very early stage.
 Some noteworthy contributions:
 
 * `lib/matrix_server/state_resolution.ex`: Implementation of version 2 of the Matrix state resolution algorithm.
+* `lib/matrix_server/state_resolution/authorization.ex`: Implementation of authorization rules for the state resolution algorithm.
 * `lib/matrix_server/room_server.ex`: A GenServer that holds and manages the state of a room.
 
 To run the server in development mode, run:
diff --git a/lib/matrix_server/event.ex b/lib/matrix_server/event.ex
index 739322a..ad2545a 100644
--- a/lib/matrix_server/event.ex
+++ b/lib/matrix_server/event.ex
@@ -28,7 +28,7 @@ defmodule MatrixServer.Event do
     }
   end
 
-  def create_room(room, %Account{localpart: localpart} = creator, room_version) do
+  def create_room(room, %Account{localpart: localpart} = creator, room_version, auth_events \\ []) do
     mxid = MatrixServer.get_mxid(localpart)
 
     %Event{
@@ -38,11 +38,12 @@ defmodule MatrixServer.Event do
         content: %{
           "creator" => mxid,
           "room_version" => room_version || MatrixServer.default_room_version()
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def join(room, %Account{localpart: localpart} = sender) do
+  def join(room, %Account{localpart: localpart} = sender, auth_events \\ []) do
     mxid = MatrixServer.get_mxid(localpart)
 
     %Event{
@@ -51,11 +52,12 @@ defmodule MatrixServer.Event do
         state_key: mxid,
         content: %{
           "membership" => "join"
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def power_levels(room, %Account{localpart: localpart} = sender) do
+  def power_levels(room, %Account{localpart: localpart} = sender, auth_events \\ []) do
     mxid = MatrixServer.get_mxid(localpart)
 
     %Event{
@@ -77,62 +79,68 @@ defmodule MatrixServer.Event do
           "notifications" => %{
             "room" => 50
           }
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def name(room, sender, name) do
+  def name(room, sender, name, auth_events \\ []) do
     %Event{
       new(room, sender)
       | type: "m.room.name",
         state_key: "",
         content: %{
           "name" => name
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def topic(room, sender, topic) do
+  def topic(room, sender, topic, auth_events \\ []) do
     %Event{
       new(room, sender)
       | type: "m.room.topic",
         state_key: "",
         content: %{
           "topic" => topic
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def join_rules(room, sender, join_rule) do
+  def join_rules(room, sender, join_rule, auth_events \\ []) do
     %Event{
       new(room, sender)
       | type: "m.room.join_rules",
         state_key: "",
         content: %{
           "join_rule" => join_rule
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def history_visibility(room, sender, history_visibility) do
+  def history_visibility(room, sender, history_visibility, auth_events \\ []) do
     %Event{
       new(room, sender)
       | type: "m.room.history_visibility",
         state_key: "",
         content: %{
           "history_visibility" => history_visibility
-        }
+        },
+        auth_events: auth_events
     }
   end
 
-  def guest_access(room, sender, guest_access) do
+  def guest_access(room, sender, guest_access, auth_events \\ []) do
     %Event{
       new(room, sender)
       | type: "m.room.guest_access",
         state_key: "",
         content: %{
           "guest_access" => guest_access
-        }
+        },
+        auth_events: auth_events
     }
   end
 
diff --git a/lib/matrix_server/quick_check.ex b/lib/matrix_server/quick_check.ex
index 09c4250..7de8a2d 100644
--- a/lib/matrix_server/quick_check.ex
+++ b/lib/matrix_server/quick_check.ex
@@ -4,9 +4,9 @@ defmodule MatrixServer.QuickCheck do
   alias MatrixServer.{Repo, Room, Account, RoomServer}
   alias MatrixServerWeb.API.CreateRoom
 
-  def create_room do
+  def create_room(name \\ nil, topic \\ nil) do
     account = Repo.one!(from a in Account, limit: 1)
-    input = %CreateRoom{}
+    input = %CreateRoom{name: name, topic: topic}
     %Room{id: room_id} = Repo.insert!(Room.create_changeset(input))
     {:ok, pid} = RoomServer.get_room_server(room_id)
     RoomServer.create_room(pid, account, input)
diff --git a/lib/matrix_server/room.ex b/lib/matrix_server/room.ex
index bb9910f..df5db54 100644
--- a/lib/matrix_server/room.ex
+++ b/lib/matrix_server/room.ex
@@ -10,7 +10,7 @@ defmodule MatrixServer.Room do
   @primary_key {:id, :string, []}
   schema "rooms" do
     field :visibility, Ecto.Enum, values: [:public, :private]
-    field :state, :map
+    field :state, {:array, {:array, :string}}
     field :forward_extremities, {:array, :string}
     has_many :events, Event, foreign_key: :event_id
   end
@@ -22,7 +22,7 @@ defmodule MatrixServer.Room do
   def create_changeset(%CreateRoom{} = input) do
     visibility = input.visibility || :public
 
-    %Room{id: generate_room_id(), forward_extremities: [], state: %{}}
+    %Room{id: generate_room_id()}
     |> changeset(%{visibility: visibility})
   end
 
diff --git a/lib/matrix_server/room_server.ex b/lib/matrix_server/room_server.ex
index 2524e77..252528b 100644
--- a/lib/matrix_server/room_server.ex
+++ b/lib/matrix_server/room_server.ex
@@ -2,6 +2,7 @@ defmodule MatrixServer.RoomServer do
   use GenServer
 
   import Ecto.Query
+  import Ecto.Changeset
 
   alias MatrixServer.{Repo, Room, Event, StateResolution}
   alias MatrixServerWeb.API.CreateRoom
@@ -24,7 +25,7 @@ defmodule MatrixServer.RoomServer do
       nil ->
         {:error, :not_found}
 
-      %Room{} ->
+      %Room{state: serialized_state_set} ->
         case Registry.lookup(@registry, room_id) do
           [{pid, _}] ->
             {:ok, pid}
@@ -32,7 +33,8 @@ defmodule MatrixServer.RoomServer do
           [] ->
             opts = [
               name: {:via, Registry, {@registry, room_id}},
-              room_id: room_id
+              room_id: room_id,
+              serialized_state_set: serialized_state_set
             ]
 
             DynamicSupervisor.start_child(@supervisor, {__MODULE__, opts})
@@ -49,49 +51,65 @@ defmodule MatrixServer.RoomServer do
   @impl true
   def init(opts) do
     room_id = Keyword.fetch!(opts, :room_id)
+    serialized_state_set = Keyword.fetch!(opts, :serialized_state_set)
+    state_event_ids = Enum.map(serialized_state_set, fn [_, _, event_id] -> event_id end)
 
-    {:ok, %{room_id: room_id, state_set: %{}}}
+    state_set =
+      Event
+      |> where([e], e.event_id in ^state_event_ids)
+      |> Repo.all()
+      |> Enum.into(%{}, fn %Event{type: type, state_key: state_key} = event ->
+        {{type, state_key}, event}
+      end)
+
+    {:ok, %{room_id: room_id, state_set: state_set}}
   end
 
   @impl true
-  def handle_call({:create_room, account, input}, _from, %{room_id: room_id} = state) do
+  def handle_call(
+        {:create_room, account,
+         %CreateRoom{room_version: room_version, name: name, topic: topic, preset: preset}},
+        _from,
+        %{room_id: room_id} = state
+      ) do
     result =
       Repo.transaction(fn ->
+        room = Repo.one!(from r in Room, where: r.id == ^room_id)
+        create_room = Event.create_room(room, account, room_version)
+        join_creator = Event.join(room, account, [create_room.event_id])
+        pls = Event.power_levels(room, account, [create_room.event_id, join_creator.event_id])
+        auth_events = [create_room.event_id, join_creator.event_id, pls.event_id]
+        name_event = if name, do: Event.name(room, account, name, auth_events)
+        topic_event = if topic, do: Event.topic(room, account, topic, auth_events)
+
         # TODO: power_level_content_override, initial_state, invite, invite_3pid
-        with room <- Repo.one!(from r in Room, where: r.id == ^room_id),
-             {:ok, create_room_id, state_set, room} <-
-               room_creation_create_room(account, input, room),
-             {:ok, join_creator_id, state_set, room} <-
-               room_creation_join_creator(account, room, state_set, [create_room_id]),
-             {:ok, pl_id, state_set, room} <-
-               room_creation_power_levels(
-                 account,
-                 room,
-                 state_set,
-                 [create_room_id, join_creator_id]
-               ),
-             {:ok, _, state_set, room} <-
-               room_creation_preset(account, input, room, state_set, [
-                 create_room_id,
-                 join_creator_id,
-                 pl_id
-               ]),
-             {:ok, _, state_set, room} <-
-               room_creation_name(account, input, room, state_set, [
-                 create_room_id,
-                 join_creator_id,
-                 pl_id
-               ]),
-             {:ok, _, state_set, _} <-
-               room_creation_topic(account, input, room, state_set, [
-                 create_room_id,
-                 join_creator_id,
-                 pl_id
-               ]) do
-          state_set
-        else
-          reason ->
+        events =
+          [create_room, join_creator, pls] ++
+            room_creation_preset(account, preset, room, auth_events) ++
+            [name_event, topic_event]
+
+        result =
+          events
+          |> Enum.reject(&Kernel.is_nil/1)
+          |> Enum.reduce_while({%{}, room}, fn event, {state_set, room} ->
+            case verify_and_insert_event(event, state_set, room) do
+              {:ok, state_set, room} -> {:cont, {state_set, room}}
+              {:error, reason} -> {:halt, {:error, reason}}
+            end
+          end)
+
+        case result do
+          {:error, reason} ->
             Repo.rollback(reason)
+
+          {state_set, room} ->
+            serialized_state_set =
+              Enum.map(state_set, fn {{type, state_key}, event} ->
+                [type, state_key, event.event_id]
+              end)
+
+            Repo.update!(change(room, state: serialized_state_set))
+            state_set
         end
       end)
 
@@ -101,46 +119,19 @@ defmodule MatrixServer.RoomServer do
     end
   end
 
-  defp room_creation_create_room(account, %CreateRoom{room_version: room_version}, room) do
-    Event.create_room(room, account, room_version)
-    |> verify_and_insert_event(%{}, room)
-  end
-
-  defp room_creation_join_creator(account, room, state_set, auth_events) do
-    Event.join(room, account)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
-  end
-
-  defp room_creation_power_levels(account, room, state_set, auth_events) do
-    Event.power_levels(room, account)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
-  end
-
   # TODO: trusted_private_chat:
   # All invitees are given the same power level as the room creator.
-  defp room_creation_preset(
-         account,
-         %CreateRoom{preset: nil},
-         %Room{visibility: visibility} = room,
-         state_set,
-         auth_events
-       ) do
+  defp room_creation_preset(account, nil, %Room{visibility: visibility} = room, auth_events) do
     preset =
       case visibility do
         :public -> "public_chat"
         :private -> "private_chat"
       end
 
-    room_creation_preset(account, preset, room, state_set, auth_events)
+    room_creation_preset(account, preset, room, auth_events)
   end
 
-  defp room_creation_preset(account, %CreateRoom{preset: preset}, room, state_set, auth_events) do
-    room_creation_preset(account, preset, room, state_set, auth_events)
-  end
-
-  defp room_creation_preset(account, preset, room, state_set, auth_events) do
+  defp room_creation_preset(account, preset, room, auth_events) do
     {join_rule, his_vis, guest_access} =
       case preset do
         "private_chat" -> {"invite", "shared", "can_join"}
@@ -148,53 +139,15 @@ defmodule MatrixServer.RoomServer do
         "public_chat" -> {"public", "shared", "forbidden"}
       end
 
-    with {:ok, _, _, _} <-
-           room_creation_join_rules(account, join_rule, room, state_set, auth_events),
-         {:ok, _, _, _} <- room_creation_his_vis(account, his_vis, room, state_set, auth_events) do
-      room_creation_guest_access(account, guest_access, room, state_set, auth_events)
-    end
-  end
-
-  defp room_creation_join_rules(account, join_rule, room, state_set, auth_events) do
-    Event.join_rules(room, account, join_rule)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
-  end
-
-  defp room_creation_his_vis(account, his_vis, room, state_set, auth_events) do
-    Event.history_visibility(room, account, his_vis)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
-  end
-
-  defp room_creation_guest_access(account, guest_access, room, state_set, auth_events) do
-    Event.guest_access(room, account, guest_access)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
-  end
-
-  defp room_creation_name(_, %CreateRoom{name: nil}, room, state_set, _) do
-    {:ok, nil, state_set, room}
-  end
-
-  defp room_creation_name(account, %CreateRoom{name: name}, room, state_set, auth_events) do
-    Event.name(room, account, name)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
-  end
-
-  defp room_creation_topic(_, %CreateRoom{topic: nil}, room, state_set, _) do
-    {:ok, nil, state_set, room}
-  end
-
-  defp room_creation_topic(account, %CreateRoom{topic: topic}, room, state_set, auth_events) do
-    Event.topic(room, account, topic)
-    |> Map.put(:auth_events, auth_events)
-    |> verify_and_insert_event(state_set, room)
+    [
+      Event.join_rules(room, account, join_rule, auth_events),
+      Event.history_visibility(room, account, his_vis, auth_events),
+      Event.guest_access(room, account, guest_access, auth_events)
+    ]
   end
 
   defp verify_and_insert_event(
-         %Event{event_id: event_id} = event,
+         event,
          current_state_set,
          %Room{forward_extremities: forward_extremities} = room
        ) do
@@ -215,9 +168,9 @@ defmodule MatrixServer.RoomServer do
           if Authorization.authorized?(event, current_state_set) do
             # We assume here that the event is always a forward extremity.
             room = Room.update_forward_extremities(event, room)
-            {:ok, event} = Repo.insert(event)
+            event = Repo.insert!(event)
             state_set = StateResolution.resolve_forward_extremities(event)
-            {:ok, event_id, state_set, room}
+            {:ok, state_set, room}
           else
             {:error, :soft_failed}
           end
diff --git a/lib/matrix_server/state_resolution.ex b/lib/matrix_server/state_resolution.ex
index 884633d..9f6cb72 100644
--- a/lib/matrix_server/state_resolution.ex
+++ b/lib/matrix_server/state_resolution.ex
@@ -264,9 +264,9 @@ defmodule MatrixServer.StateResolution do
   end
 
   def update_state_set(
-         %Event{type: event_type, state_key: state_key} = event,
-         state_set
-       ) do
+        %Event{type: event_type, state_key: state_key} = event,
+        state_set
+      ) do
     Map.put(state_set, {event_type, state_key}, event)
   end
 
diff --git a/lib/matrix_server_web/controllers/auth_controller.ex b/lib/matrix_server_web/controllers/auth_controller.ex
index 5ce6366..2723aee 100644
--- a/lib/matrix_server_web/controllers/auth_controller.ex
+++ b/lib/matrix_server_web/controllers/auth_controller.ex
@@ -44,7 +44,7 @@ defmodule MatrixServerWeb.AuthController do
 
   def register(conn, %{"auth" => _}) do
     # Other login types are unsupported for now.
-    put_error(conn, :forbidden)
+    put_error(conn, :unrecognized, "Only m.login.dummy is supported currently.")
   end
 
   def register(conn, _params) do
@@ -87,8 +87,11 @@ defmodule MatrixServerWeb.AuthController do
             |> put_status(200)
             |> json(data)
 
-          {:error, error} ->
+          {:error, error} when is_atom(error) ->
             put_error(conn, error)
+
+          {:error, _} ->
+            put_error(conn, :unknown)
         end
 
       _ ->
@@ -98,6 +101,6 @@ defmodule MatrixServerWeb.AuthController do
 
   def login(conn, _params) do
     # Other login types and identifiers are unsupported for now.
-    put_error(conn, :unknown)
+    put_error(conn, :unrecognized, "Only m.login.password is supported currently.")
   end
 end
diff --git a/lib/matrix_server_web/controllers/room_controller.ex b/lib/matrix_server_web/controllers/room_controller.ex
index 2ccd9b4..fc00b43 100644
--- a/lib/matrix_server_web/controllers/room_controller.ex
+++ b/lib/matrix_server_web/controllers/room_controller.ex
@@ -15,9 +15,10 @@ defmodule MatrixServerWeb.RoomController do
         input = apply_changes(cs)
 
         # TODO: refactor
-        %Room{id: room_id} = Repo.insert!(Room.create_changeset(input))
-        {:ok, pid} = RoomServer.get_room_server(room_id)
-        RoomServer.create_room(pid, account, input)
+        # Room.create(account, input)
+        # %Room{id: room_id} = Repo.insert!(Room.create_changeset(input))
+        # {:ok, pid} = RoomServer.get_room_server(room_id)
+        # RoomServer.create_room(pid, account, input)
 
         conn
         |> put_status(200)
diff --git a/lib/matrix_server_web/plug/error.ex b/lib/matrix_server_web/plug/error.ex
index 9a53e5c..a2ff711 100644
--- a/lib/matrix_server_web/plug/error.ex
+++ b/lib/matrix_server_web/plug/error.ex
@@ -2,7 +2,7 @@ defmodule MatrixServerWeb.Plug.Error do
   import Plug.Conn
   import Phoenix.Controller, only: [json: 2]
 
-  @error_code_and_message %{
+  @error_map %{
     bad_json: {400, "M_BAD_JSON", "Bad request."},
     user_in_use: {400, "M_USER_IN_USE", "Username is already taken."},
     invalid_username: {400, "M_INVALID_USERNAME", "Invalid username."},
@@ -13,9 +13,9 @@ defmodule MatrixServerWeb.Plug.Error do
     missing_token: {401, "M_MISSING_TOKEN", "Access token required."}
   }
 
-  def put_error(conn, error) do
-    {status, errcode, errmsg} = @error_code_and_message[error]
-    data = %{errcode: errcode, error: errmsg}
+  def put_error(conn, error, msg \\ nil) do
+    {status, errcode, default_msg} = @error_map[error]
+    data = %{errcode: errcode, error: msg or default_msg}
 
     conn
     |> put_status(status)
diff --git a/priv/repo/migrations/20210729143750_change_room_state_to_array.exs b/priv/repo/migrations/20210729143750_change_room_state_to_array.exs
new file mode 100644
index 0000000..80304e8
--- /dev/null
+++ b/priv/repo/migrations/20210729143750_change_room_state_to_array.exs
@@ -0,0 +1,10 @@
+defmodule MatrixServer.Repo.Migrations.ChangeRoomStateToArray do
+  use Ecto.Migration
+
+  def change do
+    alter table(:rooms) do
+      remove :state, :map, default: %{}, null: false
+      add :state, {:array, {:array, :string}}, default: [], null: false
+    end
+  end
+end