sasl_getopt_t is used to retrieve an option, often mechanism specific, from the
application. An example of this is requested what KERBEROS_V4 srvtab
file to use.
plugin_name is the plugin this value if for.
option is a string representing the option. A common option that all server
applications should handle is
method for checking plaintext passwords. See the administrators guide
for a full description of this option.
Memory management of options supplied by the getopt callback should be
done by the application, however, any requested option must remain available
until the callback is no longer valid. That is, when sasl_dispose is called for a
the connection it is associated with, or sasl_done is called for global callbacks.