LiveView & End-to-end encryption

The situation

Hi there! I’m working on a live view app right now that encrypts sensitive user content (text and images) using the browser’s subtlecrypto Javascript APIs.

Showing Content

For text, I implemented a custom HTML element that can take a base64 string of encrypted text, decrypt it, and render it to the page. For images, it takes a link to the image, downloads it, decrypts it, and then renders and image tag with the decrypted data. This is working well!

Creating Content

This gets trickier. When the user writes text or uploads an image, I want to show the plain text, and a preview of the image in the browser. I’d love to do as little custom coding as possible around form interactions, meaning I’d love to just let Live View do its magic with form submission, validation, etc, but I’d love to have a Javascript Hook from Live View that would let me transform the form data before it reaches the server. I’d encrypt the body text and any uploaded images, and then let Live View continue on as if I hadn’t done anything at all.

The Question

I’m not aware of any existing LiveView JS hooks that would let me do something like this. What’s the cleanest and simplest architecture you can think of to put as much of the work as possible on Live View, while still encrypting text and images before they get sent to the server?