Add ErrorHandler for API Auth.

CHANGELOG.org

@@ -63,3 +63,5 @@
     Add the auth pipeline for the Link API path.
 ** 0.8.3 <2023-08-11 Fri>
     Add tests for user login.
+** 0.8.4 <2023-08-12 Sat>
+    Add ErrorHandler for API Auth.

lib/link_shortener_web/auth/error_handler.ex

@@ -0,0 +1,10 @@
+defmodule LinkShortenerWeb.Auth.ErrorHandler do
+  import Plug.Conn
+
+  def auth_error(conn, {type, _reason}, _opts) do
+    body = Poison.encode!(%{error: to_string(type)})
+    conn
+    |> put_resp_content_type("application/json")
+    |> send_resp(401, body)
+  end
+end