The value that comes after Basic in the authorization header is username:password base64-encoded.
See for instance https://en.wikipedia.org/wiki/Basic_access_authentication on how this works
From your screenshot, I can easily see your username and password (good thing that you posted dummy values), for instance by putting them into this decoder: https://www.base64decode.org/
How the authorization process works is not added in Mendix to the generation of the swagger file.
You can manually change the swagger file and add an authorization-description. Of course this will get overwritten every time you regenerate the swagger file.
You can also add it to the description of the specific service. That will get added to the swagger file upon generation.
As description there is only this https://docs.mendix.com/refguide/published-rest-service#3-2-authentication-methods