Configure ASPNETCORE_URLS for Blazor Wasm

[smirkingsquiggly]

I'm running a Blazor Wasm application and Identity Server with Aspire 9.2.
In order to setup a CORS policy in Identity Server, I'd like to pass the client-side address (ASPNETCORE_URLS env variable) of the Blazor app to Identity Server as an environment variable.

IResourceBuilder<ProjectResource> idSrv = builder.AddProject<Projects.IdentityServer>("identity");

IResourceBuilder<ProjectResource> frontend = builder.AddProject<Projects.BlazorApp>("frontend")
    .WithReference(idSrv);

idSrv.WithEnvironment("blazorEndpoint", ???);

How do I grab the value of ASPNETCORE_URLS from the Blazor app or configure the value?
I've tried to configure it in launchSettings.json but it's not being picked up. When running, this env variable has a random port number in it.