I'm following the instructions mentioned in the list some years ago about using a subclass of ConnectAuth using ConnectAuthDefault as a sample: "You could create your own subclass of ConnectAuth, and override the method:" public abstract int callback(Credential[] cred); What I'm doing is just "copying" ConnectAuthDefault to ConnectAuthAlternate and using exactly the same code. The thing is that the callback defined in that class never fires: ConnectAuth defaultAuth = new ConnectAuthAlternate(); try{ conn = new Connect("qemu+ssh://student@10.164.1.21/system", defaultAuth, 0); } catch (LibvirtException e){ System.out.println("exception caught:"+e); System.out.println(e.getError()); } It works as expected, asks for the user password and connects successfully but it never reaches the callback defined in ConnectAuthAlternate (aka ConnectAuthDefault): @Override public int callback(Credential[] cred) { BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); [...] I'm using libvirt-java 0.5.1, JNA 4.1 and the current libvirt version that comes with ubuntu 13.10: 1.1.1-0ubuntu8.5 Could you give some light about this?. Sergio.