Add federation API

Add signing keys fed API request

lib/matrix_server/account.ex

@@ -102,7 +102,7 @@ defmodule MatrixServer.Account do
   end
 
   defp try_get_localpart("@" <> rest = user_id) do
-    case String.split(rest, ":") do
+    case String.split(rest, ":", parts: 2) do
       [localpart, _] -> localpart
       _ -> user_id
     end

lib/matrix_server/application.ex

@@ -13,7 +13,8 @@ defmodule MatrixServer.Application do
       MatrixServerWeb.Endpoint,
       {Registry, keys: :unique, name: MatrixServer.RoomServer.Registry},
       {DynamicSupervisor, name: MatrixServer.RoomServer.Supervisor, strategy: :one_for_one},
-      MatrixServer.SigningServer
+      MatrixServer.SigningServer,
+      {Finch, name: MatrixServerWeb.HTTPClient}
     ]
 
     Supervisor.start_link(children, name: MatrixServer.Supervisor, strategy: :one_for_one)