Auth process for my application

Question

Hello, I am trying for almost 2 days to understand something that should be quite simple.
I am building a very simple web app that has a simple form. Once the form is submitted all I want to do is to save the content in my oneDrive as a new file. That's all!!!
But all the auth flows I see are required a login pop which won't be possible in this case since I want to collect all the form submissions into my one drive.
So I tried the client_credentials grant type but then I get an error that my token is not in the context when I am trying to write files into my one drive.

Please point me in the right direction what I need to do? it's a very simple process. just to save files on my oneDrive as a background process from my web app.
Using Javascript and running on the browser. I did this flow on many other platforms and that never been so complicated.

Thanks a lot