The current WebAssembly code works well using the cors-anywhere CORS proxy server. I've quickly tried a couple of other CORS proxy servers and they do not work. We need to investigate such others and support them as much as possible.

We will need changes to js_maybe_convert_url which modifies request URLs to send them via the CORS proxy based on environment variables. It is essentially a string transform function (string in, string out) that combines the request URL and CORS proxy URL, but different CORS proxies require different transforms. For example, some need the protocal for the request URL to be included and some do not. Probably the way forward here is to support some simple variable substitution syntax in the GIT_CORS_PROXY, perhaps of the form {protocol} or similar.