As the person quoted right at the beginning, I should probably  
contribute my findings here.

I don't believe that ticket refresh is an issue. I can quite happily  
refresh, destroy, or replace my Kerberos credentials from under a  
running GSSAPI context, without causing that context to break.

The issue (if there is an issue) is that Heimdal and MIT's behaviour  
differ when the initiator's credentials do actually expire. Heimdal  
allows the context to continue to be used for wrapping operations  
past expiry - MIT expires the context, and calls to wrap() or unwrap 
() fail. This difference in behaviour is an issue when using SASL  
applications with security layers, as the only way to renew the  
context is to reconnect to the server. In addition, many applications  
have inadequate error handling around their security layer  
implementations.

I suspect that the current MIT behaviour is correct. Whilst there's  
no explicit language in RFC2743, it suggests that the length of time  
for which the context will be valid depends on credential lifetime.

Simon.