Web App using Google Apps Script not working with distributed URL

Question

What the program does: I have written a simple Google Apps Script that retrieves unread emails from a label in the Gmail account currently logged in, and returns the number of those emails, and displays it on the website.

Problem: This program works when I created a web app from the computer I developed it on, and run it from the website. However, if I copy the URL and distribute it to another computer that is logged in as another Google account, it doesn't work.

Code:

/*Sample.gs*/ 
function doGet(e){
    return HtmlService.createHtmlOutputFromFile('Run.html');
}

function GetUnreadCount(sourceLabel){
    return GmailApp.getUserLabelByName(sourceLabel).getUnreadCount();
}

function Main()
{   
    /*For testing, return unread email count from "CustomerA" label of Gmail*/
    return GetUnreadCount("CustomerA");
}

.

/*Run.html*/
<!DOCTYPE html> 
<html>
  <head>
    <base target="_top">
    <script>
        function CallGetUnreadCount() {

          document.getElementById('Messages').innerHTML = 'Counting...';

          google.script.run
            .withSuccessHandler(onSuccess)
            .withFailureHandler(onFailure)
            .Main();          
        }

        function onSuccess(UnreadCount) 
        {
          document.getElementById('Messages').innerHTML = "There are " + UnreadCount + " unread emails.";
        }

        function onFailure(error) 
        {
          document.getElementById('Messages').innerHTML = "Err: " + error.message;
        }

    </script>
  </head>
  <body>
    <div>
        <h1 id="Messages">Count # of unread emails</h1>
    </div>
    <div>
        <button type="button" onclick='CallGetUnreadCount();' id="CountButton">Count Unread Emails</button> 
    </div>
  </body>
</html>

This program works fine if I run it on the computer I wrote this script on. However, if I deploy it as a web app, and distribute the URL (ending with /exec), and run it on another computer that has logged in as a different Gmail account, it always returns 0 even when there are unread emails in CustomerA label. What confuses me is, this same program works on another computer if I create a new project on that computer and copy-paste the above code into a .gs file and an html file, and deploy as a web app.

Why does the same program work if each computer deploys the web app on their own, but not work if I distribute the URL?

Answer 1

When Deploying as web app (Publish > Deploy as web app), there are a few options to configure:

• Execute the app as: Can be either Me, or User accessing the web app. For your case, you must use the later to make it work as you expect.
• Who has access to this app: Can be either Only myselft, Anyone within your domain or Anyone. You have to make sure it's either the 2nd or 3rd option, depending on your needs, so that the user can properly execute it.