React + ASP.Net Core 3：CORS 对预检请求的响应未通过访问控制检查：无'Access-Control-Allow-Origin'标头

Question

我正在尝试设置一个反应前端来与.net后端通信。但是，我似乎被困在设置的cors上。下面我有来自后端项目的启动代码以及来自前端的代码。我已经遵循了多个指南，但我不确定我在哪里搞砸了，这以前在我的本地主机上有效，但在部署到云时则无效。(我遵循的指南：https://learn.microsoft.com/en-us/aspnet/core/security/cors?view=aspnetcore-3.1 和 https://code-maze.com/enabling-cors-in-asp-net-core/(

感谢您的帮助！

来自 React 应用程序控制台的错误： CORS 策略已阻止从源"https://frontend.azurewebsites.net"获取"https://backend.azurewebsites.net/api/accountcredentials"的访问：对预检请求的响应未通过访问控制检查：请求的资源上不存在"访问控制-允许源"标头。如果不透明响应满足您的需求，请将请求的模式设置为"no-cors"，以便在禁用 CORS 的情况下获取资源。

项目中 asp.net 启动代码：

public void ConfigureServices(IServiceCollection services)
{
services.AddMvc()
.AddNewtonsoftJson();
services.AddSingleton<UserService>();
services.AddSingleton<AccountService>();
services.AddCors(o => o.AddPolicy("ReactPolicy", builder =>
{
builder.AllowAnyOrigin() //dev
//.WithOrigins("http://localhost:3007") // dev
//.WithOrigins("https://frontend.azurewebsites.net")
.AllowAnyMethod()
.AllowAnyHeader()
.AllowCredentials();
}));
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
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.UseHttpsRedirection();
app.UseRouting(routes =>
{
routes.MapControllers();
});
app.UseCors("ReactPolicy");
app.UseAuthorization();
}

控制器类的属性：

[Produces("application/json")]
[Route("api/[controller]")]
[ApiController]
[EnableCors("ReactPolicy")]

Answer 1

试试这个方法：

readonly string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";
public void ConfigureServices(IServiceCollection services)
{
...
services.AddCors(options =>
{
options.AddPolicy(MyAllowSpecificOrigins,
builder =>
{
builder.SetIsOriginAllowed(isOriginAllowed: _ => true).AllowAnyHeader().AllowAnyMethod().AllowCredentials();
});
});
...
}

public void Configure(IApplicationBuilder app, IHostEnvironment env)
{
...
app.UseForwardedHeaders(new ForwardedHeadersOptions
{
ForwardedHeaders = ForwardedHeaders.XForwardedFor |
ForwardedHeaders.XForwardedProto
});
app.UseCors(MyAllowSpecificOrigins);
...
} 

编辑MyAllowSpecificOrigins到您的 CORS 名称