It is unclear how to get an access token for a script to use the API

I’m trying to use the simple send.sig.request script to send signature requests, but it is not at all clear how to get the access token. The JWT seems like overkill as I don’t need to impersonate everyone, just access as a single user, but I don’t want to deal with popping up web pages and whatnot for consent - it just needs to send the request. The instructions say to setup a redirect uri, but it’s not at all clear what the uri is supposed to do when whatever redirects to it…

Thanks for any help...