diff --git a/lib/matrix_server.ex b/lib/matrix_server.ex
index f389b35..a497a71 100644
--- a/lib/matrix_server.ex
+++ b/lib/matrix_server.ex
@@ -41,6 +41,16 @@ defmodule MatrixServer do
     end
   end
 
+  # TODO Eventually move to regex with named captures.
+  def get_localpart(id) do
+    with [part, _] <- String.split(id, ":", parts: 2),
+         {_, localpart} <- String.split_at(part, 1) do
+      localpart
+    else
+      _ -> nil
+    end
+  end
+
   # https://elixirforum.com/t/22709/9
   def has_duplicates?(list) do
     list
diff --git a/lib/matrix_server/signing_server.ex b/lib/matrix_server/signing_server.ex
index ea166a7..44b07d5 100644
--- a/lib/matrix_server/signing_server.ex
+++ b/lib/matrix_server/signing_server.ex
@@ -26,32 +26,11 @@ defmodule MatrixServer.SigningServer do
     {:ok, %{public_key: public_key, private_key: private_key}}
   end
 
-  # https://blog.swwomm.com/2020/09/elixir-ed25519-signatures-with-enacl.html
   @impl true
-  def handle_call(
-        {:sign_object, object},
-        _from,
-        %{private_key: private_key} = state
-      ) do
-    case MatrixServer.encode_canonical_json(object) do
-      {:ok, json} ->
-        signature =
-          json
-          |> :enacl.sign_detached(private_key)
-          |> MatrixServer.encode_unpadded_base64()
-
-        signature_map = %{@signing_key_id => signature}
-        servername = MatrixServer.server_name()
-
-        signed_object =
-          Map.update(object, :signatures, %{servername => signature_map}, fn signatures ->
-            Map.put(signatures, servername, signature_map)
-          end)
-
-        {:reply, {:ok, signed_object}, state}
-
-      {:error, _msg} ->
-        {:reply, {:error, :json_encode}, state}
+  def handle_call({:sign_object, object}, _from, %{private_key: private_key} = state) do
+    case sign_object(object, private_key) do
+      {:ok, signature} -> {:reply, {:ok, signature, @signing_key_id}, state}
+      {:error, _reason} -> {:reply, :error, state}
     end
   end
 
@@ -61,6 +40,18 @@ defmodule MatrixServer.SigningServer do
     {:reply, [{@signing_key_id, result}], state}
   end
 
+  # https://blog.swwomm.com/2020/09/elixir-ed25519-signatures-with-enacl.html
+  defp sign_object(object, private_key) do
+    with {:ok, json} <- MatrixServer.encode_canonical_json(object) do
+      signature =
+        json
+        |> :enacl.sign_detached(private_key)
+        |> MatrixServer.encode_unpadded_base64()
+
+      {:ok, signature}
+    end
+  end
+
   # TODO: not sure if there is a better way to do this...
   defp get_keys do
     raw_priv_key =
diff --git a/lib/matrix_server_web/authenticate_server.ex b/lib/matrix_server_web/authenticate_server.ex
index ca58acc..2b16bb2 100644
--- a/lib/matrix_server_web/authenticate_server.ex
+++ b/lib/matrix_server_web/authenticate_server.ex
@@ -1,75 +1,50 @@
 defmodule MatrixServerWeb.AuthenticateServer do
-  import Ecto.Changeset
+  import MatrixServerWeb.Plug.Error
 
   alias MatrixServer.SigningServer
-  alias Ecto.Changeset
 
   @auth_header_regex ~r/^X-Matrix origin=(?<origin>.*),key="(?<key>.*)",sig="(?<sig>.*)"$/
 
-  defmodule SignedJSON do
-    use Ecto.Schema
+  def authenticate(
+        %Plug.Conn{
+          body_params: body_params,
+          req_headers: headers,
+          request_path: path,
+          method: method,
+          query_string: query_string
+        }
+      ) do
+    object_to_sign = %{
+      uri: path <> "?" <> URI.decode_www_form(query_string),
+      method: method,
+      destination: MatrixServer.server_name()
+    }
 
-    import Ecto.Changeset
+    object_to_sign =
+      if method != "GET", do: Map.put(object_to_sign, :content, body_params), else: object_to_sign
 
-    @primary_key false
-    embedded_schema do
-      field :method, :string
-      field :uri, :string
-      field :origin, :string
-      field :destination, :string
-      field :content, :map
-      field :signatures, :map
-    end
+    object_fun = &Map.put(object_to_sign, :origin, &1)
 
-    def changeset(params) do
-      %__MODULE__{}
-      |> cast(params, [:method, :uri, :origin, :destination, :content, :signatures])
-      |> validate_required([:method, :uri, :origin, :destination])
-    end
+    authenticate_with_headers(headers, object_fun)
   end
 
-  def authenticated?(%Plug.Conn{body_params: params}) do
-    with %Changeset{valid?: true} = cs <- SignedJSON.changeset(params),
-         input <- apply_changes(cs) do
-      verify_signature(input)
-    else
-      _ -> false
-    end
-  end
+  defp authenticate_with_headers(headers, object_fun) do
+    headers
+    |> parse_authorization_headers()
+    |> Enum.find(:error, fn {origin, _, sig} ->
+      # TODO: fetch actual signing keys for origin from cache/key store.
+      {_, signing_key} = SigningServer.get_signing_keys() |> hd()
+      object = object_fun.(origin)
 
-  defp verify_signature(%SignedJSON{signatures: signatures, origin: origin} = input) do
-    if Map.has_key?(signatures, origin) do
-      # TODO: fetch actual signing keys from cache/key store.
-      signing_keys = SigningServer.get_signing_keys() |> Enum.into(%{})
-
-      found_signatures =
-        Enum.filter(signatures[origin], fn {key, _} ->
-          case String.split(key, ":", parts: 2) do
-            [algorithm, _] -> algorithm == "ed25519"
-            _ -> false
-          end
-        end)
-        |> Enum.map(fn {key_id, sig} ->
-          if Map.has_key?(signing_keys, key_id) do
-            {key_id, sig, signing_keys[key_id]}
-          end
-        end)
-        |> Enum.reject(&Kernel.is_nil/1)
-
-      with [{_, sig, signing_key} | _] <- found_signatures,
-           {:ok, raw_sig} <- MatrixServer.decode_base64(sig),
-           serializable_input <- MatrixServer.to_serializable_map(input),
-           {:ok, encoded_input} <- MatrixServer.encode_canonical_json(serializable_input) do
-        :enacl.sign_verify_detached(raw_sig, encoded_input, signing_key)
+      with {:ok, raw_sig} <- MatrixServer.decode_base64(sig),
+           {:ok, encoded_object} <- MatrixServer.encode_canonical_json(object) do
+        :enacl.sign_verify_detached(raw_sig, encoded_object, signing_key)
       else
         _ -> false
       end
-    else
-      false
-    end
+    end)
   end
 
-  # TODO: Not actually needed?
   def parse_authorization_headers(headers) do
     headers
     |> Enum.filter(&(elem(&1, 0) == "authorization"))
@@ -77,9 +52,10 @@ defmodule MatrixServerWeb.AuthenticateServer do
       Regex.named_captures(@auth_header_regex, auth_header)
     end)
     |> Enum.reject(&Kernel.is_nil/1)
-    |> Enum.reduce(%{}, fn %{"origin" => origin, "key" => key, "sig" => sig}, acc ->
-      Map.update(acc, origin, %{key => sig}, &Map.put(&1, key, sig))
+    |> Enum.map(fn %{"origin" => origin, "key" => key, "sig" => sig} ->
+      {origin, key, sig}
     end)
+    |> Enum.filter(fn {_, key, _} -> String.starts_with?(key, "ed25519:") end)
   end
 
   defmacro __using__(opts) do
@@ -89,10 +65,14 @@ defmodule MatrixServerWeb.AuthenticateServer do
       def action(conn, _) do
         action = action_name(conn)
 
-        if action not in unquote(except) and
-             not MatrixServerWeb.AuthenticateServer.authenticated?(conn) do
-          IO.puts("Not authorized!")
-          apply(__MODULE__, action, [conn, conn.params])
+        if action not in unquote(except) do
+          case MatrixServerWeb.AuthenticateServer.authenticate(conn) do
+            {origin, _key, _sig} ->
+              conn = Plug.Conn.assign(conn, :origin, origin)
+              apply(__MODULE__, action, [conn, conn.params])
+            :error ->
+              put_error(conn, :unauthorized, "Signature verification failed.")
+          end
         else
           apply(__MODULE__, action, [conn, conn.params])
         end
diff --git a/lib/matrix_server_web/federation/query_controller.ex b/lib/matrix_server_web/federation/query_controller.ex
new file mode 100644
index 0000000..0568356
--- /dev/null
+++ b/lib/matrix_server_web/federation/query_controller.ex
@@ -0,0 +1,55 @@
+defmodule MatrixServerWeb.Federation.QueryController do
+  use MatrixServerWeb, :controller
+  use MatrixServerWeb.AuthenticateServer
+
+  import MatrixServerWeb.Plug.Error
+  import Ecto.Query
+
+  alias MatrixServer.{Repo, Account}
+
+  defmodule ProfileRequest do
+    use Ecto.Schema
+
+    import Ecto.Changeset
+
+    @primary_key false
+    embedded_schema do
+      field :user_id, :string
+      field :field, :string
+    end
+
+    def validate(params) do
+      %__MODULE__{}
+      |> cast(params, [:user_id, :field])
+      |> validate_required([:user_id])
+      |> validate_inclusion(:field, ["displayname", "avatar_url"])
+      |> tap(fn
+        %Ecto.Changeset{valid?: true} = cs -> {:ok, apply_changes(cs)}
+        _ -> :error
+      end)
+    end
+  end
+
+  def profile(conn, params) do
+    with %ProfileRequest{user_id: user_id} <- ProfileRequest.validate(params) do
+      if MatrixServer.get_domain(user_id) == MatrixServer.server_name() do
+        localpart = MatrixServer.get_localpart(user_id)
+
+        case Repo.one(from a in Account, where: a.localpart == ^localpart) do
+          %Account{} ->
+            # TODO: Return displayname and avatar_url when we implement them.
+            conn
+            |> put_status(200)
+            |> json(%{})
+
+          nil ->
+            put_error(:not_found, "User does not exist.")
+        end
+      else
+        put_error(:not_found, "Wrong server name.")
+      end
+    else
+      _ -> put_error(conn, :bad_json)
+    end
+  end
+end
diff --git a/lib/matrix_server_web/federation/test_controller.ex b/lib/matrix_server_web/federation/test_controller.ex
deleted file mode 100644
index 37d7e8b..0000000
--- a/lib/matrix_server_web/federation/test_controller.ex
+++ /dev/null
@@ -1,10 +0,0 @@
-defmodule MatrixServerWeb.Federation.TestController do
-  use MatrixServerWeb, :controller
-  use MatrixServerWeb.AuthenticateServer
-
-  def test(conn, _params) do
-    conn
-    |> put_status(200)
-    |> json(%{})
-  end
-end
diff --git a/lib/matrix_server_web/federation_client.ex b/lib/matrix_server_web/federation_client.ex
index 5036544..26f07c2 100644
--- a/lib/matrix_server_web/federation_client.ex
+++ b/lib/matrix_server_web/federation_client.ex
@@ -20,26 +20,27 @@ defmodule MatrixServerWeb.FederationClient do
     Tesla.get(client, RouteHelpers.key_path(Endpoint, :get_signing_keys))
   end
 
-  def test_server_auth(client) do
-    origin = "localhost:4001"
-    destination = "localhost:4000"
-    path = RouteHelpers.test_path(Endpoint, :test)
+  # TODO: Create tesla middleware to add signature and headers.
+  def query_profile(client, server_name, user_id, field \\ nil) do
+    origin = MatrixServer.server_name()
+    path = RouteHelpers.query_path(Endpoint, :profile) |> Tesla.build_url(user_id: user_id)
+    path = if field, do: Tesla.build_url(path, field: field), else: path
 
-    params = %{
-      method: "POST",
+    object_to_sign = %{
+      method: "GET",
       uri: path,
       origin: origin,
-      destination: destination,
-      content: %{"hi" => "hello"}
+      destination: server_name
     }
 
-    {:ok, signed_object} = MatrixServer.SigningServer.sign_object(params)
-    auth_headers = create_signature_authorization_headers(signed_object, origin)
+    {:ok, signature, key_id} = MatrixServer.SigningServer.sign_object(object_to_sign)
+    signatures = %{origin => %{key_id => signature}}
+    auth_headers = create_signature_authorization_headers(signatures, origin)
 
-    Tesla.post(client, path, signed_object, headers: auth_headers)
+    Tesla.get(client, path, headers: auth_headers)
   end
 
-  defp create_signature_authorization_headers(%{signatures: signatures}, origin) do
+  defp create_signature_authorization_headers(signatures, origin) do
     Enum.map(signatures[origin], fn {key, sig} ->
       {"Authorization", "X-Matrix origin=#{origin},key=\"#{key}\",sig=\"#{sig}\""}
     end)
diff --git a/lib/matrix_server_web/plug/error.ex b/lib/matrix_server_web/plug/error.ex
index d65abad..3fb7b12 100644
--- a/lib/matrix_server_web/plug/error.ex
+++ b/lib/matrix_server_web/plug/error.ex
@@ -11,10 +11,11 @@ defmodule MatrixServerWeb.Plug.Error do
     unknown: {400, "M_UNKNOWN", "An unknown error occurred."},
     invalid_room_state:
       {400, "M_INVALID_ROOM_STATE", "The request would leave the room in an invalid state."},
+    unauthorized: {400, "M_UNAUTHORIZED", "The request was unauthorized."},
     unknown_token: {401, "M_UNKNOWN_TOKEN", "Invalid access token."},
     missing_token: {401, "M_MISSING_TOKEN", "Access token required."},
     not_found: {404, "M_NOT_FOUND", "The requested resource was not found."},
-    room_alias_exists: {409, "M.UNKNOWN", "The given room alias already exists."}
+    room_alias_exists: {409, "M_UNKNOWN", "The given room alias already exists."}
   }
 
   def put_error(conn, {error, msg}), do: put_error(conn, error, msg)
diff --git a/lib/matrix_server_web/router.ex b/lib/matrix_server_web/router.ex
index ff7ac8a..3ebc8b6 100644
--- a/lib/matrix_server_web/router.ex
+++ b/lib/matrix_server_web/router.ex
@@ -56,7 +56,7 @@ defmodule MatrixServerWeb.Router do
   scope "/_matrix", MatrixServerWeb.Federation do
     pipe_through :authenticate_server
 
-    post "/test", TestController, :test
+    get "/federation/v1/query/profile", QueryController, :profile
   end
 
   scope "/", MatrixServerWeb.Client do