Add channel to be joined

lib/birdy_chat_web/channels/server_channel.ex

@@ -0,0 +1,35 @@
+defmodule BirdyChatWeb.ServerChannel do
+  use BirdyChatWeb, :channel
+
+  @impl true
+  def join("server:" <> server_id, payload, socket) do
+    if authorised?(payload, server_id) do
+      {:ok, socket}
+    else
+      {:error, %{reason: "unauthorised"}}
+    end
+  end
+
+  @impl true
+  def handle_in("new_message", {:binary, message}, socket) do
+    result = :erlang.binary_to_term(message, [:safe])
+
+    # TODO: Add validation that this is the right server.
+    case BirdyChat.Message.validate(result) do
+      {:ok, changeset} ->
+        case BirdyChat.MessageWriter.write(changeset.changes) do
+          :ok ->
+            {:reply, {:ok, {:binary, message}}, socket}
+        end
+    end
+  end
+
+  # Simple token-based authentication. Servers should use the same Phoenix secret key so they will
+  # have the basis for generating tokens.
+  defp authorised?(%{"token" => token}, server_id) do
+    case Phoenix.Token.verify(BirdyChatWeb.Endpoint, "serverAuth", token, max_age: 86400) do
+      {:ok, id} -> id == server_id
+      {:error, :invalid} -> false
+    end
+  end
+end