final DefaultRemoteProxySettings remoteProxySettings = new DefaultRemoteProxySettings();
remoteProxySettings.setHttpProxySettings(httpProxy);
remoteProxySettings.setHttpsProxySettings(httpsProxy);
customizer.applyProxyConfig(builder, remoteProxySettings);
final CredentialsProvider credentialsProvider = builder.getCredentialsProvider();
assertThat(credentialsProvider.getCredentials(AuthScope.ANY), notNullValue(Credentials.class));
assertThat(credentialsProvider.getCredentials(AuthScope.ANY).getUserPrincipal().getName(), equalTo("user"));