/* This function is used by authentication drivers to output a challenge
to the SMTP client and read the response line. This version does not use base
-64 encoding for the text on the 334 line. It is used by the SPA and dovecot
-authenticators.
+64 encoding for the text on the 334 line. It is used by the SPA, dovecot
+and gsasl authenticators.
Arguments:
aptr set to point to the response (which is in big_buffer)