Android Picasso library, How to add authentication headers?

Since Picasso 2.5.0 OkHttpDownloader class has been changed, assuming you are using OkHttp3 (and so picasso2-okhttp3-downloader), so you have to do something like this:

OkHttpClient client = new OkHttpClient.Builder()
        .addInterceptor(new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Request newRequest = chain.request().newBuilder()
                        .addHeader("X-TOKEN", "VAL")
                        .build();
                return chain.proceed(newRequest);
            }
        })
        .build();

Picasso picasso = new Picasso.Builder(context)
        .downloader(new OkHttp3Downloader(client))
        .build();

Source: https://github.com/square/picasso/issues/900

See bryant1410's answer for a more up-to-date solution.

Something like this does the job for setting an API-key header:

public class CustomPicasso {

    private static Picasso sPicasso;

    private CustomPicasso() {
    }

    public static Picasso getImageLoader(final Context context) {
        if (sPicasso == null) {
            Picasso.Builder builder = new Picasso.Builder(context);
            builder.downloader(new CustomOkHttpDownloader());
            sPicasso = builder.build();
        }
        return sPicasso;
    }

    private static class CustomOkHttpDownloader extends OkHttpDownloader {

        @Override
        protected HttpURLConnection openConnection(final Uri uri) throws IOException {
            HttpURLConnection connection = super.openConnection(uri);
            connection.setRequestProperty(Constants.HEADER_X_API_KEY, "MY_API_KEY");
            return connection;
        }
    }
}

You can also add Authentication as suggested in the documentation of OkHttp

Just add this client

final OkHttpClient client = new OkHttpClient.Builder()
                .authenticator(new Authenticator() {
                    @Override
                    public Request authenticate(Route route, Response response) throws IOException {
                        String credential = okhttp3.Credentials.basic("user", "pw");
                        return response.request().newBuilder()
                                .header("Authorization", credential)
                                .build();
                    }
                })
                .build();

to Picasso like this:

final Picasso picasso = new Picasso.Builder(this)
                .downloader(new OkHttp3Downloader(client))
                .build();
Picasso.setSingletonInstance(picasso);

The only dependency needed is:

compile 'com.jakewharton.picasso:picasso2-okhttp3-downloader:1.0.2'

It's working

        OkHttpClient okHttpClient = new OkHttpClient.Builder()
                           .authenticator(new Authenticator()
                           {
                               @Override
                               public Request authenticate(Route route, Response response) throws IOException
                               {
                                   String credential =  Credentials.basic("username","password");
                                   return response.request().newBuilder()
                                           .header("Authorization", credential)
                                           .build();
                               }
                           }).build();

                   Picasso picasso = new Picasso.Builder(OnDemandImageCaptureActivity.this)
                           .downloader(new OkHttp3Downloader(okHttpClient))
                           .build();
                        picasso.load("http://example.com/abc.jpeg").into(ivcamera);

dependency:

compile 'com.squareup.picasso:picasso:2.5.2'
compile 'com.jakewharton.picasso:picasso2-okhttp3-downloader:1.1.0'