File Drop via API authentication for link for use in http client

I want my mobile app to upload files to a file drop folder. I got the shared link, but how can I get the according authentication key used for that folder / link programatically?

When I use the browser for uploading to that folder, I can figure out the authentication key as the PUT method uses it in the Authentication header (“Basic <key>”). But my clients are not capable of finding that, so I nee a programmatic solution to determine this key from the given shared link (to the upload folder).

Thank you!