Re: [kitten] SASL's idea of "additional data" in a protocol

Hi Rick,

On 19/03/2020 08:49, Rick van Rein wrote:
> Hello,
>
> RFC 4422 states that there may be additional data with a success.  I
> don't think I have ever seen this in any protocol or mechanism.  Am I
> correct that there is no reason in practice to add it to a protocol
> embedding of SASL?

Actually, this is being used. Look for example at SCRAM (RFC 5802), the 
last message from the server (containing the v= attribute) can be sent 
as "additional data with success". It is always better to allow for this 
in a SASL protocol profile in order to save an extra round trip. I.e. if 
this feature is not supported by a protocol, the server will have to 
send it as a regular SASL response, to which the client will have to 
respond with an empty challenge, which will then be responded to by the 
server with just successful outcome (with no data).

Best Regards,

Alexey

> The text is,
>
>     Some mechanisms specify that the server is to send additional data to
>     the client when indicating a successful outcome.  Protocols may
>     provide an optional additional data field in the outcome message to
>     carry this data.  Where the mechanism specifies that the server is to
>     return additional data with the successful outcome, the protocol
>     provides an optional additional data field in the outcome message,
>     and the server uses this field, the exchange is shortened by one
>     round-trip:
>
> Thanks,
>   -Rick
>
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