: Change to "Reply-Message AVP" usage in Diameter EAP

Tom Hiller and Glen Zorn have found an issue in Diameter EAP that they
would like to fix in AUTH48.

The issue relates to an inconsistency between RADIUS/EAP as specified
in RFC 3579, and Diameter with respect to the Reply-Message AVP.

We now have:

2.8.3.  Displayable Messages

    The Reply-Message AVP [NASREQ] contains text which may be displayed
    to the user.  Note that the NAS does not necessarily have any
    facility for actually sending these messages to the user.  In any
    case, the NAS MUST NOT manufacture any EAP packets (such as
    EAP-Request/Notification) from Reply-Message AVPs.

Tom has suggested:

2.8.3.  Displayable Messages

The Reply-Message AVP [NASREQ] MUST NOT be included in any Diameter
message containing an EAP-Payload AVP.

Here is the text in RFC 3579, Section 2.6.5:

2.6.5.  Displayable Messages

   The Reply-Message attribute, defined in [RFC2865], Section 5.18,
   indicates text which may be displayed to the peer.  This is similar
   in concept to EAP Notification, defined in [RFC2284].  When sending a
   displayable message to a NAS during an EAP conversation, the RADIUS
   server MUST encapsulate displayable messages within
   EAP-Message/EAP-Request/Notification attribute(s).  Reply-Message
   attribute(s) MUST NOT be included in any RADIUS message containing an
   EAP-Message attribute.  An EAP-Message/EAP-Request/Notification
   SHOULD NOT be included within an Access-Accept or Access-Reject
   packet.

   . . .

   To avoid these problems, a NAS receiving a Reply-Message attribute
   from the RADIUS server SHOULD silently discard the attribute, rather
   than attempting to translate it to an EAP Notification Request.