sasl_client_init() initializes SASL. It must be called before any calls to
sasl_client_start. This call initializes all SASL client drivers
(e.g. authentication mechanisms). These are usually found in the
/usr/lib/sasl2 directory but the directory may be overridden with the
SASL_PATH environment variable.
callbacks specifies the base callbacks for all client connections. See the sasl_callbacks man page for more information