BasicAuthInterceptor.java

import android.support.annotation.NonNull;
import com.example.app.BuildConfig;
import okhttp3.Credentials;
import okhttp3.Interceptor;
import okhttp3.Request;
import okhttp3.Response;

import java.io.IOException;

public class BasicAuthInterceptor implements Interceptor {

    private static final String AUTH_USER = BuildConfig.AUTH_USER;
    private static final String AUTH_PASS = BuildConfig.AUTH_PASS;

    @Override
    public Response intercept(@NonNull final Chain chain) throws IOException {
        final Request request = chain.request();
        final Request newRequest = request.newBuilder()
                .header("Authorization", Credentials.basic(AUTH_USER, AUTH_PASS))
                .build();

        return chain.proceed(newRequest);
    }

}