I believe the problem with this solution today is that I used Slacks Legacy Token to authenticate my http requests, but I don’t believe you are allowed to create new legacy tokens anymore. I believe everything must be oAuth now and I’m not sure how to do that.
I know this isn’t a complete answer, but hopefully it will help get you started down the right path.
Requesting that this functionality be added is one option, since they have the API authentication already figured out. However, even if they don’t add that functionality, you may be able to use it to authenticate with Slack, and then somehow get your token from them. If you can get the oAuth Token that they receive from Slack during the authentication process, then you should be able to put that in the “Token” field in my first photo and authenticate that way.