ASPReactDemo/Api/Program.cs

using Api.SignalR;
using Microsoft.AspNetCore.SignalR;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddOpenApi();
builder.Services.AddSignalR();
builder.Services.AddHostedService<SignalRSendService>();
builder.Services.AddSingleton<IUserIdProvider, UserProvider>();
builder.Services.AddOpenApiDocument(config => { config.Title = "NSwag Demo API"; });
builder.Services.AddCors(options =>
{
    options.AddDefaultPolicy(policy =>
    {
        policy.WithOrigins("http://localhost:5173")
            .AllowAnyHeader()
            .AllowAnyMethod()
            .AllowCredentials();
    });
});

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    app.UseOpenApi();
    app.UseSwaggerUi();
}

app.UseHttpsRedirection();
app.UseCors();

var summaries = new[]
{
    "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
};

app.MapGet("/weatherforecast", async () =>
    {
        var hub = app.Services.GetRequiredService<IHubContext<WeatherUpdateHub>>();
        for (var i = 0; i < 100; i++)
        {
            await hub.Clients.All.SendAsync("ProgressUpdate", "None", $$"""{"percentage": "{{i}}", "message": "{{DateTime.Now.Millisecond}}"}""");
            await Task.Delay(100);
        }


        var forecast = Enumerable.Range(1, 2500).Select(index =>
                new WeatherForecast
                (
                    DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
                    Random.Shared.Next(-20, 55),
                    summaries[Random.Shared.Next(summaries.Length)]
                ))
            .ToArray();

        return forecast;
    })
    .WithName("GetWeatherForecast");


// Add SignalR hub
app.MapHub<WeatherUpdateHub>("/WeatherUpdateHub");

app.Run();

record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)
{
    public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
}