class OmniAuth::Builder

def provider(klass, *args, **opts, &block)
  if klass.is_a?(Class)
    middleware = klass
  else
    begin
      middleware = OmniAuth::Strategies.const_get(OmniAuth::Utils.camelize(klass.to_s).to_s, false)
    rescue NameError
      raise(LoadError.new("Could not find matching strategy for #{klass.inspect}. You may need to install an additional gem (such as omniauth-#{klass})."))
    end
  end
  use middleware, *args, **options.merge(opts), &block
end