如果你在IIS上托管，一个可能的原因是你得到这个是因为IIS阻塞选项动词。我为此花了将近一个小时:

一个明显的迹象是在OPTIONS请求期间出现404错误。

要解决这个问题，您需要显式地告诉IIS不要阻止OPTIONS请求。

进入请求过滤:

确保允许使用OPTIONS:

或者，只是做一张网。配置如下设置:

<system.webServer>
    <security>
        <requestFiltering>
            <verbs>
                <remove verb="OPTIONS" />
                <add verb="OPTIONS" allowed="true" />
            </verbs>
        </requestFiltering>
    </security>
</system.webServer>

ASP。NET核心Web API

在ConfigureServices中添加services.AddCors();之前services.AddControllers ();

在“配置”中添加UseCors

app.UseCors(x => x
.AllowAnyOrigin()
.AllowAnyMethod()
.AllowAnyHeader());

在我设法在最琐碎的CORS问题上浪费了两个小时后，一些故障排除技巧:

If you see CORS policy execution failed logged... Don't assume that your CORS policy is not executing properly. In fact, the CORS middleware works, and your policy is executing properly. The only thing this badly worded message means is that the request's origin doesn't match any of the allowed origins (see source), i.e. the request is disallowed. The origin check (as of ASP.NET Core 5.0) happens in a very simple way... i.e. case-sensitive ordinal string comparison (see source) between the strings you provided via WithOrigins() and what exists in HttpContext.Request.Headers[Origin]. CORS can fail if you set an allowed origin with a trailing slash /, or if it contains uppercase letters. (In my case I did in fact accidentally copy the host with a trailing slash.)

对于“c# - ASP Net Core Web API (Net Core 3.1 LTS)”，它为我工作…

在Startup.cs文件:

在“ConfigureServices”函数中添加以下代码:

services.AddCors(options =>
{
    options.AddPolicy("CorsPolicy",
        builder => builder.AllowAnyOrigin()
        .AllowAnyMethod()
        .AllowAnyHeader());
});

注意:在“CorsPolicy”的情况下，你可以改变你喜欢的或在“Startup”类中使用全局变量。

在“Configure”函数中添加以下代码:

app.UseCors("CorsPolicy");

检查函数的调用顺序，它应该是这样的:

if (env.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}

app.UseHttpsRedirection();
app.UseRouting();
app.UseCors("CorsPolicy");
app.UseAuthentication();
app.UseAuthorization();

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

最后，在你的控制器类中，将下面的代码添加到你的函数之上:

[EnableCors("CorsPolicy")]

例如:

[EnableCors("CorsPolicy")]
[HttpPost("UserLoginWithGoogle")]
public async Task<ActionResult<Result>> UserLoginWithGoogle([FromBody] TokenUser tokenUser)
{            
    Result result = await usersGoogleHW.UserLoginWithGoogle(tokenUser.Token);
    return new JsonResult(result);
}

注意:“CorsPolicy”必须在启动和控制器中匹配。

祝你好运……

步骤1:我们需要微软. aspnetcore . cors包在我们的项目。安装请进入“Tools -> NuGet Package Manager -> Manage NuGet Packages For Solution”。搜索“Microsoft.AspNetCore.Cors”，安装软件包。

步骤2:我们需要将CORS注入到容器中，以便应用程序可以使用它。在Startup.cs类中，让我们转到ConfigureServices方法并注册CORS。

因此，在我们的服务器应用程序中，让我们进入Controllers -> homeconcontroller .cs，并将EnableCors装饰器添加到Index方法(或您特定的控制器和动作):

更多详情请点击这里

ASP。NET Core 6:

var  MyAllowSpecificOrigins = "_myAllowSpecificOrigins";

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddCors(options =>
{
    options.AddPolicy(name: MyAllowSpecificOrigins,
                      builder =>
                      {
                          builder.WithOrigins("http://example.com",
                                              "http://www.contoso.com");
                      });
});

// services.AddResponseCaching();

builder.Services.AddControllers();

var app = builder.Build();
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();

app.UseCors(MyAllowSpecificOrigins);

app.UseAuthorization();

app.MapControllers();

app.Run();

更多样品请参考官方文档。

ASP。NET Core 3.1和5.0:

你必须在应用程序启动时在ConfigureServices方法中配置CORS策略:

public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(o => o.AddPolicy("MyPolicy", builder =>
    {
        builder.WithOrigins("http://example.com")
               .AllowAnyMethod()
               .AllowAnyHeader();
    }));

    // ...
}

builder中的CorsPolicyBuilder允许您根据需要配置策略。你现在可以使用这个名字将策略应用到控制器和动作上:

[EnableCors("MyPolicy")]

或者把它应用到每一个请求上:

public void Configure(IApplicationBuilder app)
{
    app.UseCors("MyPolicy");

    // ...

    // This should always be called last to ensure that
    // middleware is registered in the correct order.
    app.UseMvc();
}