[android] How to set custom header in Volley Request

If what you need is to post data instead of adding the info in the url.

public Request post(String url, String username, String password, 
      Listener listener, ErrorListener errorListener) {
  JSONObject params = new JSONObject();
  params.put("user", username);
  params.put("pass", password);
  Request req = new Request(
     Method.POST,
     url,
     params.toString(),
     listener,
     errorListener
  );

  return req;
}

If what you want to do is edit the headers in the request this is what you want to do:

// could be any class that implements Map
Map<String, String> mHeaders = new ArrayMap<String, String>();
mHeaders.put("user", USER);
mHeaders.put("pass", PASSWORD);
Request req = new Request(url, postBody, listener, errorListener) {
  public Map<String, String> getHeaders() {
    return mHeaders;
  }
}