Rails, given an AWS S3 URL, how to use a controller to send_data / file to the requestor

Given an Amazon S3 URL, or any URL that is a direct URL to a file. In my controller, given this URL, I want to send the user the file, whatever it is w/o redirecting.

Is this possible?

If I understand your question correctly, I don't think that's possible from your end. That's why many sites say "right click to save" or something along those lines. Some sites even have links to videos that say "click to download" but when I click the link they start streaming. These are due to MY settings (ie. the settings on the user's client). You can't control that.

If what you're trying to do is HIDE the location of a file...

Send files back to the user - Usually, static files can be retrieved by using the direct URL and circumventing your Rails application. In some situations, however, it can be useful to hide the true location of files, particularly if you're sending something of value (e-books, for example). It may be essential to only send files to logged in users too. send_file makes it possible. It sends files in 4096 byte chunks, so even large files can be sent without slowing the system down.

From an old blog post