sasl_server_init() initializes SASL. It must be called before any calls to
sasl_server_start, and only once per process.
This call initializes all SASL mechanism 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 (or at compile time).
callbacks specifies the base callbacks for all client connections. See
the sasl_callbacks man page for more information.
appname is the name of the application. It is used for where to find the
default configuration file.