Query on an optional(?) element in SAMLResponse

Hello,

  We  had a long discussion internally and decided we'll send AuthnContextClassRef optionally in our SAMLResponse. 

  We'll be  a SAML 2.0 IdP supporting only web-browser SSO (supporting HTTP-Redirect at our end and post binding for SP).

  My reading of Oasis core tells me that AuthnContextClassRef is optional, Is this correct?

<AuthnStatement>
 -----
 <AuthnInstant>         required
    <SessionIndex>         optional

   <SessionNotOnOrAfter>  optional
   <SubjectLocality       optional 

      <adddress>         optional  

      <DNSName>          optional
  <AuthnContext>         required

    <AuthnContextClassRef>  optional
    <AuthnContextDecl>      optional
    <AuthenticatingAuthority>  zero or more

 

But have been advised by actual implementors that we should send it always. (http://lists.labs.libre-entreprise.org/pipermail/lasso-devel/2009-September/002456.html -  

Thanks to Benjamin of Lasso for answering all my questions)

What are your comments?

Thanks in advance.

--Bhaskar.