When creating HttpClients the code just calls HttpClientBuilder.create().build(); e.g.

This means that it is not possible to configure a proxy when using the PhotosLibraryClient and if this is required by the network setup it results in a java.net.SocketException: Network is unreachable (connect failed). The easiest fix would be to just call .useSystemProperties before calling .build on HttpClientBuilder and that would allow developers to specify a proxy using the System Properties.