Error Massage: Access to XMLHttpRequest at 'URL' from origin 'URL' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I have a .net5 web_api application and frontend develop using reactjs. This web_api work perfectly on localhost. I used ionos windows hosting. when I host my web_app on IIS server then the error comes.

I have tried on web.config file. Like that

 <httpProtocol>
  <customHeaders>
     <add name="Access-Control-Allow-Origin" value="*" />
     <add name="Access-Control-Allow-Methods" value="GET,PUT,POST,DELETE,OPTIONS" />
     <add name="Access-Control-Allow-Headers" value="Content-Type" />
   </customHeaders>
 </httpProtocol>

I have tried on startup.cs file. Like that

        services.AddCors(opt =>
        {
            opt.AddPolicy(name: MyAllowSpecificOrigins,
                policy =>
                {
                    policy.WithOrigins("http://localhost:3000")
                    .WithHeaders(HeaderNames.ContentType, "x-custom-header", HeaderNames.CacheControl)
                    .WithMethods("POST", "PUT", "DELETE", "GET", "OPTIONS")
                    .AllowCredentials()
                    .SetPreflightMaxAge(TimeSpan.FromSeconds(2520))
                    .Build();
                });
        });

and

        services.AddCors(options =>
        {
            options.AddDefaultPolicy(builder =>
            {
                builder.WithOrigins("http://localhost:3000")
                .AllowAnyHeader()
                .AllowAnyMethod()
                .AllowCredentials();
            });
        });

I'm trying to solve this error various way. But i can't do it.

Please help me to solve this.

CodePudding user response：

I created a new asp.net core 5 api project and enabled cors policy by adding code in startup.cs like below, and then publish the project to IIS in my virtual machine. I called the api in my asp.net core MVC project and it worked well for me. I think you may follow this

public void ConfigureServices(IServiceCollection services)
{

    services.AddControllers();
    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebApi", Version = "v1" });
    });
    //add cors service and send the policy
    services.AddCors(options =>
    {
        options.AddPolicy(name: "mypolicy", builder =>
        {
            builder.WithOrigins("https://localhost:44323/")
            .AllowAnyHeader()
            .AllowAnyMethod()
            .AllowCredentials();
        });
    });
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
        app.UseSwagger();
        app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", "WebApi v1"));
    }

    app.UseHttpsRedirection();

    app.UseRouting();
    app.UseCors("mypolicy");//use cors policy by this line


    app.UseAuthorization();

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

CodePudding user response：

In the end, I solved this error ☺️. this error comes from "WebDAVModule". I just remove this module from web.config file.

Add modules-remover before handlers.

web.config

<modules>
  <remove name="WebDAVModule" />
</modules>
<handlers>
</handlers>