Update authentication method

slices/admin/repos/user_repo.rb

@@ -0,0 +1,17 @@
+module Admin
+  module Repos
+    class UserRepo < Adamantium::Repo[:users]
+      commands :create
+
+      def exists(id)
+        !!users
+          .where(id: id)
+          .one
+      end
+
+      def by_email(email:)
+        users.where(email: email).one
+      end
+    end
+  end
+end