Include a Blazor Webassembly project into an existing ASP.NET Core project

Add Microsoft.AspNetCore.Components.WebAssembly.Server nuget to the ASP.NET Core application.

Reference the Blazor WebAssembly application from the ASP.NET Core application.

<Project Sdk="Microsoft.NET.Sdk.Web">
<!-- ... -->
<ItemGroup>
    <!-- ... -->
    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly.Server" Version="3.2.1" />
</ItemGroup>

<ItemGroup>
    <!-- ... -->
    <ProjectReference Include="..\MyBlazorApp.csproj" />
</ItemGroup>
<!-- ... -->
</Project>

Edit the Startup file of the ASP.NET Core application:

1. Add UseWebAssemblyDebugging if running in development mode (see sample below).
2. Call the UseBlazorFrameworkFiles.
3. Add MapFallbackToFile("index.html") routing.

namespace MyApp
{
    public class Startup
    {
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                // ...
                app.UseWebAssemblyDebugging();                  // this
            }

            // ...
            app.UseBlazorFrameworkFiles();                      // this

            app.UseEndpoints(endpoints =>
            {
                // ...
                endpoints.MapFallbackToFile("index.html");      // this
            });
        }
    }
}

Then edit the launchSettings.json, add inspectUri like so:

{
    // ...
    "profiles": {
    "IIS Express": {
        // ...
        "inspectUri": "{wsProtocol}://{url.hostname}:{url.port}/_framework/debug/ws-proxy?browser={browserInspectUri}"
    },
    "MyApp": {
        // ...
        "inspectUri": "{wsProtocol}://{url.hostname}:{url.port}/_framework/debug/ws-proxy?browser={browserInspectUri}"
    }
    }
}