Example of a getting a file from Telegram without exposing your Bot Token using nodeJS and express. TelegramClient.getFileDetails is a call to the Telegram getFile api. The file is then requested and the response is pipped into response sent back to the user

TelegramDocumentProxy.js

router.get('/:documentId/*', (req, res) => {
  var documentId = req.params.documentId;
  if(documentId){
    TelegramClient.getFileDetails(documentId).then((fileDetails) => {
      var fileUrl = TelegramClient.getTelegramFileUrl(fileDetails.result.file_path);
     request(fileUrl)
      .on('response', (response) => {
        if (response.statusCode === 200) {
              res.writeHead(200, {
                  'Content-Type': response.headers['content-type']
              });
              response.pipe(res);
          } else {
              res.writeHead(response.statusCode);
              res.end();
          }
        });
    });
  }
  else{
    res.statusCode = 500;
    res.json({
      error: 'Not a valid file ID',
    });
  }

});