Re: Heirarchical error codes

[Doug Royer <Doug.Royer@xxxxxxx>]

> Date: Fri, 19 Mar 1999 10:46:39 -0500 (EST)
> From: Rob Earhart <rob@andrew.cmu.edu>
> 
> > Are you thinking of some sort of CAPABILITY list that the client sends the
> > server, and a similar set of capabilities that the server returns based on
> > what it received from the client??
> 
>   Almost; I'd rather see both simply send capability lists when the
> connection is initialized.  For instance, at session startup, one might
> see
> 
>   C: * CAPABILITY CAP XMLCAL
>   S: * CAPABILITY CAP SASL ("KERBEROS_V4" "GSSAPI" "DIGEST-MD5") TLS
> 
> (using * instead of a normal tag because these aren't commands; they're
> information which doesn't require a reply.) 

Untagged can get messy if we allow capability in multiple states as
shown in the straw-man draft (and I hope we keep that).  I am hopping
that you can only see the authentication mechanisms in the connected
state.  And the rest of the capabilities after authentication.

For example, now that I know who you (authenticated entity) are, you
also have the capability to use x, y, and z. I could also see a CS
implementation sending different results to an authenticated CUA
depending if they were inside or outside of a firewall.

So the client would need to know how to authenticate initially, then
could query the CS after authentication for more capabilities.
Requireing a tagged capability command?

>   The server probably shouldn't restrict its list based on what it gets
> from the client; it's useful to see everything the server's capable of.
> After this exchange, both sides know what the other's capable of dealing
> with, and can restrict what they speak to the subset of the capabilities
> they know about for which the other side has announced support.

Supporting a capability is one issue, how do we handle MUST for
an implementation? What if for security reasons a particular 
CS implementation requires that TLS MUST be used. How do we
say that? Do we care?

-Doug
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