从受密码保护的sharepoint下载文件，android studio

Question

我需要从我需要登录才能访问的sharepoint下载文件。这是我的代码，但每次我收到错误说：下载错误：服务器返回HTTP 401未经授权。 mFileToDownload包含url。登录相关代码位于Download Task \ doInBackground。

private void DownloadNecessaryFiles () {
    mProgressDialog = new ProgressDialog(HomeActivity.this);
    mProgressDialog.setMessage("Downloading. Please wait...");
    mProgressDialog.setIndeterminate(true);
    mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
    mProgressDialog.setCancelable(true);

    mCEVACommon.VerifyStoragePermissions (HomeActivity.this);

    final DownloadTask downloadTask = new DownloadTask(HomeActivity.this);
    downloadTask.execute(mFileToDownload);

    mProgressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
        @Override
        public void onCancel(DialogInterface dialog) {
            downloadTask.cancel(true);
        }
    });

}

private class DownloadTask extends AsyncTask<String, Integer, String> {

    private Context context;
    private PowerManager.WakeLock mWakeLock;

    public DownloadTask(Context context) {
        this.context = context;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                getClass().getName());
        mWakeLock.acquire();
        mProgressDialog.show();
    }

    @Override
    protected String doInBackground(String... sUrl) {
        String username = "user", password = "user";

        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            connection = (HttpURLConnection) url.openConnection();

            final String authString = username + ":" + password;
            connection.setRequestProperty("Authorization", "Basic " + Base64.encode (authString.getBytes(),Base64.NO_WRAP));

            connection.connect();

            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                return "Server returned HTTP " + connection.getResponseCode()
                        + " " + connection.getResponseMessage();
            }

            int fileLength = connection.getContentLength();

            input = connection.getInputStream();
            output = new FileOutputStream(mRootAPPDataDirectory + "/downloaded.csv");

            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {

                if (isCancelled()) {
                    input.close();
                    return null;
                }
                total += count;

                if (fileLength > 0)
                    publishProgress((int) (total * 100 / fileLength));
                output.write(data, 0, count);
            }
        } catch (Exception e) {
            return e.toString();
        } finally {
            try {
                if (output != null)
                    output.close();
                if (input != null)
                    input.close();
            } catch (IOException ignored) {
            }

            if (connection != null)
                connection.disconnect();
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        // if we get here, length is known, now set indeterminate to false
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setMax(100);
        mProgressDialog.setProgress(progress[0]);
    }

    @Override
    protected void onPostExecute(String result) {
        mWakeLock.release();
        mProgressDialog.dismiss();
        if (result != null)
            Toast.makeText(context, "Download error: " + result, Toast.LENGTH_LONG).show();
        else
            Toast.makeText(context, "File downloaded", Toast.LENGTH_SHORT).show();
    }
}

有任何想法吗？