This is a rough demo illustrating how the PayPal-Auth-Assertion header is composed and decomposed.
It follows the implementation docs on https://developer.paypal.com/docs/multiparty/issue-refund/.
Note that you will need to have Node.js installed.
Install the dependencies...
npm install
...then start the app:
npm run dev
Navigate to localhost:8080. You should see your app running.
To create an optimised version of the app:
npm run build
With Vercel
Install vercel
if you haven't already:
npm install -g vercel
Then, from within your project folder:
cd public
vercel deploy --name my-project