app/views/saml_idp/idp/saml_post.html.erb
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
</head>
<body onload="document.forms[0].submit();" style="visibility:hidden;">
<%= form_tag(@saml_acs_url) do %>
<%= hidden_field_tag("SAMLResponse", @saml_response) %>
<%= submit_tag "Submit" %>
<% end %>
</body>
</html>