Android OkHttp with Basic Authentication-open source projects square/okhttp
 Jesse Wilson
Try using OkAuthenticator:
client.setAuthenticator(new OkAuthenticator() {
  @Override public Credential authenticate(
      Proxy proxy, URL url, List challenges) throws IOException {
    return Credential.basic("scott", "tiger");
  }
  @Override public Credential authenticateProxy(
      Proxy proxy, URL url, List challenges) throws IOException {
    return null;
  }
});