SignalR & Cross-Domain on AzureWebsite

Question

I am trying to use SignalR on an AzureWebsites app and I'm stuck on a cross-domain issue.

Starting from this tutorial, everything works fine when run locally or when run on azurewebsites: https://docs.microsoft.com/en-us/aspnet/core/tutorials/signalr?view=aspnetcore-3.1&tabs=visual-studio

No changes to the tutorial code, all as is.

If I move the client to a different domain than the SignalR server app it no longer works.

I'm researching the issue but any pointers would be very appreciated.

Answer 1

What you need to do is firstly configure your SignalR application like this:

public void ConfigureServices(IServiceCollection services)
{
   services.AddCors(cfg =>
           {
                cfg.AddDefaultPolicy(policy =>
                {
                     policy.WithOrigins(Configuration.GetSection("AuthServer:DomainBaseUrl").Get<string[]>())
                     .AllowAnyHeader()
                     .AllowAnyMethod()
                     .AllowCredentials()
                     .SetIsOriginAllowed((_) => true)
                     .SetIsOriginAllowedToAllowWildcardSubdomains();
                });
           });
    services.AddSignalR(options =>
           {
                options.ClientTimeoutInterval = TimeSpan.FromHours(1);
                options.EnableDetailedErrors = true;
                options.HandshakeTimeout = TimeSpan.FromMinutes(10);
                options.KeepAliveInterval = TimeSpan.FromMinutes(5);
           });
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
      {
       // Code removed for brevity
       app.UseCors();

           app.UseEndpoints(endpoints =>
           {
                endpoints.MapControllers();
           });
}

---

NOTE: The line below

policy.WithOrigins(Configuration.GetSection("AuthServer:DomainBaseUrl").Get<string[]>())

is used to get the list of domains (array of domains) to allow for CORS from the config file and is.

---

And in your Client Application do this as well, hoping your client app is an ASP.NET Core MVC app too.

    public void ConfigureServices(IServiceCollection services)
{
   services.AddCors(cfg =>
           {
                cfg.AddDefaultPolicy(policy => {
                     policy.AllowAnyHeader();
                     policy.AllowAnyMethod();
                     policy.AllowAnyOrigin();
                     policy.WithMethods();
                });
           });
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
      {
       // Code removed for brevity
       app.UseCors();

           app.UseEndpoints(endpoints =>
           {
                endpoints.MapControllers();
           });
}

---

I hope this helps your situation.