Convert Excel VBA App Online

I have a small Excel workbook that currently relies on a VBA-driven GUI. I now need the same experience available through a browser so colleagues can access it without downloading the file.

The workbook is fairly simple: a user enters 2 parameters into input boxes, presses a "calculate" button, and some straightforward calculations are run, to output 2 sets of results from the calculations.

Key requirements
• Technology: please build it with JavaScript. I am open to the specific stack—plain JS, React, Vue, Svelte, or similar—but the finished code must run in any modern browser and be easy to host on a standard Linux server (Node.js or static + serverless functions are both fine).
• Functionality to replicate:
– Data-input forms that mirror the existing Excel userforms.
– All underlying calculations and processing logic; the numbers produced must match the spreadsheet results one-for-one.
- Recreation of current GUI, appropriate for PC or mobile access/use

• Access control: basic user authentication is required so only registered users can reach the app. A simple email + password flow or OAuth sign-in is acceptable; whatever you implement, I need clear instructions on adding or removing users.

Deliverables
1. Source code (front-end and any back-end/API components).
2. A hosted demo or deployment script so I can test online.
3. README with setup steps, environment variables, and a brief mapping of Excel modules to JS modules so future maintenance is straightforward.
4. Confirmation that sample calculations match the original workbook.