AMQPCBS: Indicating that multiple challenge-responses are required to transmit token set

If the token set exceeds the frame size for sasl-init, then additional sasl-challenge and sasl-response pairs are required to send the remaining tokens.

Multiple approaches are possible. WD3 uses a simple strawman to encourage discussion. When the server has received all the tokens based on the token count, it stops sending sasl-challenge and sends a sasl-outcome.

Other options include:

• The equivalent of the transfer more field is added to the response data:

RESPONSE = TOKEN-COUNT 1*TOKEN MORE

to indicate whether additional sasl-challenge and sasl-response frames are required to complete the exchange.

• A "magic" value like NUL NUL could follow the last token and signal completion.

• The server always sends an "empty" sasl-challenge and the client responds with an "empty" sasl-response when the exchange is complete. This is especially inefficient if all the tokens are sent in the sasl-init.