basicauth_interceptor_retrofit2.java

String credentials = "username:password";
final String basic =
        "Basic " + Base64.encodeToString(credentials.getBytes(), Base64.NO_WRAP);

OkHttpClient httpClient = new OkHttpClient();
httpClient.interceptors().clear();

List<Interceptor> interceptors = new ArrayList<>();
interceptors.add(new Interceptor() {
    @Override
    public Response intercept(Interceptor.Chain chain) throws IOException {
        Request original = chain.request();

        Request request = original.newBuilder()
                .header("Accept", "application/json")
                .header("Authorization", basic)
                .method(original.method(), original.body()).build();

        Response response = chain.proceed(request);
        return response;
    }
});

if (BuildConfig.DEBUG) {
    HttpLoggingInterceptor logInterceptor = new HttpLoggingInterceptor();
    logInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
    interceptors.add(logInterceptor);
}

httpClient.interceptors().addAll(interceptors);