sasl_auxprop_request will request that the SASL library obtain properties from any auxiliary
property plugins that might be installed (such as the users home directory
from an LDAP server for example). Such lookup occurs just after username
canonicalization is complete. Therefore, the request should be made before
the call to sasl_server_start(3), but after the call to sasl_server_new(3).
conn the sasl_conn_t for which the request is being made.
propnames a NULL-terminated array of property names to request. Note that this
array must persist until a call to sasl_dispose on the sasl_conn_t.