The provided HTML form auto-POSTs the SAMLResponse on page load (triggered by Javascript). I wonder why this was preferred over a redirect? References: https://github.com/lawrencepit/ruby-saml-idp/blob/master/app/controllers/saml_idp/idp_controller.rb#L26 https://github.com/lawrencepit/ruby-saml-idp/blob/master/app/views/saml_idp/idp/saml_post.html.erb