Trouble downloading files in Google Apps Script web app after Chrome update

Question

I've had a Google Apps Script web app running for a bit over a year which gave users an option to download a csv file. It worked perfectly fine, although in the console it gave a warning about downloading from an iFrame being deprecated.

After updating Chrome, I now get the following error when trying to download:

Download is disallowed. The frame initiating or instantiating the download is sandboxed, but the flag ‘allow-downloads’ is not set. See https://www.chromestatus.com/feature/5706745674465280 for more details.

When following the above link, it provides the following information:

Chrome is planning on removing this capability - i.e. Chrome is going to block all downloads initiated from or instantiated in a sandboxed iframe by default. The embedder may add "allow-downloads" to the sandbox attributes list to opt in. This allows content providers to restrict malicious or abusive downloads.

How can I add "allow-downloads" to the sandbox attributes in the Google Apps Script environment? Alternatively, is there a workaround to enable downloading files?

Answer 1

It is discussed here https://issuetracker.google.com/issues/157368720 that HtmlService.XFrameOptionsMode.ALLOWALL should set allow-downloads on GAS web app sandbox. We should watch this issue for changes.

Answer 2

Include sandbox="allow-downloads" in your iframe tag, which contains the code that is used for downloading the CSV file.