Hi Mario,
I would recommend installing the following extension in VS Code: IdentityNow Extensions for Visual Studio Code. This will let you more easily edit your source without needing to use Postman for these operations.
Once you’ve connected your tenant, you can create a new rule and can select the Web Service before operation rule:
You can leverage the samples from the post you linked to get started on the rule. If you right click this rule in VS Code, you can edit the script in standard java, rather than needing to translate it and put it in sourceCode/script.
To then link it back to a specific operation, you can go into the source in VS Code, and add the following tag into each HTTP operation you want the rule to run on:
"beforeRule": "<insert rule name>"
Hope this helps!