Picasso is an awesome library for downloading and caching images.  If the images that you need to download require authentication you can do that by specifying a custom Downloader class. If you do this you can no longer use the with method to initialise Picasso.

This is explained if you read the javadocs but if you’re like me you may have been stumped for a short while because it looked like your custom downloader was not working. In my case I needed to add a bearer authentication header to the image request so I did this:

Picasso.Builder builder = new Picasso.Builder(getContext());

builder.downloader(new OkHttpDownloader(getContext()) {
    @Override
    protected HttpURLConnection openConnection(Uri uri) throws IOException {
        HttpURLConnection connection = super.openConnection(uri);
        connection.addRequestProperty("Authorization", "Bearer: <token>");
        return connection;
    }
});

Once you have done this you can use Picasso as normal, but don’t use the with method or that will undo the changes you have made.

builder.build()
        .load(Uri.parse("https://example.com/image.png"))
        .into(imageView);