Digits with custom button

gistfile1.java

final AuthCallback authCallback = new AuthCallback() {
            @Override
            public void success(DigitsSession digitsSession, String s) {
                //Success !!
            }

            @Override
            public void failure(DigitsException e) {
                //sad :(
            }
        };
button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Digits.authenticate(authCallback);
            }
        });

It does not work