[jdev] ask the variable meaning in some Jabberd datastructure

[angus_lan]

   i am now  leaning Jabberd2,in the following structure,what is the authnid and authzid mean when using in SASL? 
typedef struct _scod_cb_creds_st {
    char        *authnid;
    char        *realm;
    char        *pass;
    char        *authzid;
} *scod_cb_creds_t;