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);
            }
        });

AuthConfig.Builder builder = new AuthConfig.Builder();

                    builder.withAuthCallBack(new AuthCallback() {
                        @Override
                        public void success(DigitsSession session, String phoneNumber) {
                            Toast.makeText(getApplicationContext(), "Authentication successful for "
                                    + phoneNumber, Toast.LENGTH_LONG).show();

                             // Do something
                        }

                        @Override
                        public void failure(DigitsException error) {
                           // Do something
                        }
                    });

                    AuthConfig authConfig = builder.build();

                    Digits.authenticate(authConfig);

It does not work