reading your question closer, Blazor WASM works like any web page. the WASM is just a resource loaded into the browser via an ajax call from the index.html. so the link to the index page should be https. blazor WASM just uses the javascript's ajax support for WebClient, so the ajax urls just need to be https. typically you set the base url in the index.html, and use relative links. The browser supplies all the https support, and you configure the browser to support your blazor hosting website.
if you are using a separate webapi site, then be sure to enable CORS, and use https:
in short you configure the blazor hosting website as https, just as if it was a regular website.
note: blazor wasm is in a sandbox and can not directly access the internet, filesystems or the browser dom. it uses javascript interop to do this. to the browser, a blazor app is just a html/javascript app that loads a WebAssembly.