SRP_VBASE_get1_by_user
srp_callback_parm->user = SRP_VBASE_get1_by_user(srp_callback_parm->vb,
SRP_user_pwd *SRP_VBASE_get1_by_user(SRP_VBASE *vb, char *username);
user = SRP_VBASE_get1_by_user(vbase, username);