Add BasicAuthDecoderPlug

lib/pleroma/plugs/basic_auth_decoder_plug.ex

@@ -0,0 +1,21 @@
+defmodule Pleroma.Plugs.BasicAuthDecoderPlug do
+  import Plug.Conn
+
+  def init(options) do
+    options
+  end
+
+  def call(conn, opts) do
+    with ["Basic " <> header] <- get_req_header(conn, "authorization"),
+         {:ok, userinfo} <- Base.decode64(header),
+         [username, password] <- String.split(userinfo, ":", parts: 2) do
+      conn
+      |> assign(:auth_credentials, %{
+        username: username,
+        password: password
+      })
+    else
+      _ -> conn
+    end
+  end
+end