public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    // ... other middleware ...

    // Make sure the CORS middleware is ahead of SignalR.
    app.UseCors(builder =>
    {
        builder.WithOrigins("https://example.com")
            .AllowAnyHeader()
            .WithMethods("GET", "POST")
            .AllowCredentials();
    });

    // ... other middleware ...
    app.UseRouting();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapHub<ChatHub>("/chatHub");
    });

    // ... other middleware ...
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    // ... other middleware ...

    // Make sure the CORS middleware is ahead of SignalR.
    app.UseCors(builder =>
    {
        builder.WithOrigins("https://example.com")
            .AllowAnyHeader()
            .WithMethods("GET", "POST")
            .AllowCredentials();
    });

    // ... other middleware ...

    app.UseSignalR(routes =>
    {
        routes.MapHub<ChatHub>("/chatHub");
    });

    // ... other middleware ...
}

CORS 提供的保护不适用于 WebSocket。 对于 Websocket 上的源限制，请阅读websocket 源限制。

CORS 提供的保护不适用于 WebSocket。 浏览器不会：

• 执行 CORS 预检请求。
• 在发出 WebSocket 请求时，遵守 Access-Control 标头中指定的限制。

但是，浏览器在发出 WebSocket 请求时会发送 Origin 标头。 应将应用程序配置为验证这些标头，以确保只允许来自预期来源的 WebSocket。

在 ASP.NET Core 2.1 及更高版本中，可以使用在 UseSignalR之前放置的自定义中间件和 Configure中的身份验证中间件来实现标题验证：

// In Startup, add a static field listing the allowed Origin values:
private static readonly HashSet<string> _allowedOrigins = new HashSet<string>()
{
    // Add allowed origins here. For example:
    "https://www.mysite.com",
    "https://mysite.com",
};

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    // ... other middleware ...

    // Validate Origin header on WebSocket requests to prevent unexpected cross-site 
    // WebSocket requests.
    app.Use((context, next) =>
    {
        // Check for a WebSocket request.
        if (string.Equals(context.Request.Headers["Upgrade"], "websocket"))
        {
            var origin = context.Request.Headers["Origin"];

            // If there is an origin header, and the origin header doesn't match 
            // an allowed value:
            if (!string.IsNullOrEmpty(origin) && !_allowedOrigins.Contains(origin))
            {
                // The origin is not allowed, reject the request
                context.Response.StatusCode = StatusCodes.Status403Forbidden;
                return Task.CompletedTask;
            }
        }

        // The request is a valid Origin or not a WebSocket request, so continue.
        return next();
    });

    // ... other middleware ...

    app.UseSignalR(routes =>
    {
        routes.MapHub<ChatHub>("/chatHub");
    });

    // ... other middleware ...
}