Access to XMLHttpRequest has been blocked origin ASP.NET CORE 2.2.0 / Angular 8 / signalr1.0.0 [(CORS Policy-Access-Control-Allow-Origin) failed]

Question

nugetPackage on .net core2.2.0:

signalr 1.0.0 + ASP.Core2.2.0

I\'m using angular to connect use signalr:

package.json: \"@aspnet/signalr\": \"1.1.0\

Answer 1

You should apply your policy in Configure method:

public void Configure 
{
    app.UseResponseCompression();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            // The default HSTS value is 30 days. You may want to change this 
            // for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }
    app.UseCors("MyPolicy");
}

UPDATE:

If you are using localhost as http://localhost:4200, then try to set it in your configuration:

public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(options => options.AddPolicy("ApiCorsPolicy", build =>
    {                
        build.WithOrigins("http://localhost:4200")
             .AllowAnyMethod()
             .AllowAnyHeader();
        }));
        // ... other code is omitted for the brevity
     }
}

And Configure method:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    app.UseCors("ApiCorsPolicy");
    app.UseHttpsRedirection();        
    app.UseMvc();
}

Answer 2

You should add your CORS like this:

services.AddCors(options =>
{
    options.AddPolicy("CorsPolicy", builder => builder.WithOrigins("http://localhost:4200")
        .AllowAnyHeader()
        .AllowAnyMethod()
        .AllowCredentials()
        .SetIsOriginAllowed((host) => true));
});

Note:

The order is important!