How to inspect file permissions served by Karma

I'm new to Karma. When I run npx karma start I see the following gets triggered:

http://localhost:9876/
http://localhost:9876/socket.io/socket.io.js
http://localhost:9876/karma.js
http://localhost:9876/socket.io/?EIO=3&transport=polling&t=MyKpKbk
http://localhost:9876/socket.io/?EIO=3&transport=polling&t=MyKpKc7&sid=lMjFEd1O8LUrK32-AAAB
http://localhost:9876/socket.io/?EIO=3&transport=polling&t=MyKpKc8&sid=lMjFEd1O8LUrK32-AAAB
ws://localhost:9876/socket.io/?EIO=3&transport=websocket&sid=lMjFEd1O8LUrK32-AAAB // returns a 101 switching protocols message
http://localhost:9876/socket.io/?EIO=3&transport=polling&t=MyKpKdy&sid=lMjFEd1O8LUrK32-AAAB
http://localhost:9876/context.html
http://localhost:9876/context.js
http://localhost:9876/esm-test-loader.js

All of these calls are successful. However, the next file it attempts to load gets rejected by my corporate proxy:

http://localhost:9876/base/node_modules/source-map-support/browser-source-map- 
support.js?d5ed9cabce4cb9162440415eea7e8484e51d1aea

First question - in the url, where does base come from? Second, can the permissions be different from my local machine to the local server where the files are served? How can I check the permissions on localhost?

Thanks for any helpful tips.