improve registration and add oauth

lib/users.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Users
+  module_function
+
+  def from_omniauth(oauth)
+    user = User.find_by(email: oauth.info.email)
+
+    return user if user
+
+    User.new(email: oauth.info.email,
+             first_name: oauth.extra.id_info.given_name,
+             last_name: oauth.extra.id_info.family_name)
+  end
+end