CORS Configuration Not Working

[williamoanta]

I am trying to configure CORS for my backend, but I still get the error:

Access to XMLHttpRequest at 'X' from origin 'Y' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Below is my code which has the proper configuration - as per the documentation and samples:

let configureCors (builder : CorsPolicyBuilder) =
    builder.AllowAnyOrigin()
           .AllowAnyMethod()
           .AllowAnyHeader()
           |> ignore

let configureApp (app : IApplicationBuilder) =
    let env = app.ApplicationServices.GetService<IHostingEnvironment>()
    
    // Development State can be set via ASPNETCORE_ENVIRONMENT Environment Variable. Checking it here.
    let env_state = env.IsDevelopment()
    logger.debug("configureApp()", [env_state], "Environment State, Development:")
    
    (match env.IsDevelopment() with
    | true  -> app.UseCors(configureCors).UseDeveloperExceptionPage()
    | false -> app.UseCors(configureCors).UseGiraffeErrorHandler errorHandler)
        .UseHttpsRedirection()
        .UseStaticFiles()
        .UseGiraffe(webApp)

let configureServices (services : IServiceCollection) =
    services.AddCors()    |> ignore
    services.AddGiraffe() |> ignore

let configureLogging (builder : ILoggingBuilder) =
    builder.AddFilter(fun l -> l.Equals LogLevel.Error)
           .AddConsole()
           .AddDebug() |> ignore

[<EntryPoint>]
let main _ =
    let contentRoot = Directory.GetCurrentDirectory()
    let webRoot     = Path.Combine(contentRoot, "WebRoot")
    WebHostBuilder()
        .UseKestrel()
        .UseContentRoot(contentRoot)
        .UseIISIntegration()
        .UseWebRoot(webRoot)        
        .UseUrls("http://0.0.0.0:8081")
        .Configure(Action<IApplicationBuilder> configureApp)
        .ConfigureServices(configureServices)
        .ConfigureLogging(configureLogging)
        .Build()
        .Run()
    0

Also the package is imported like this:
<PackageReference Include="Microsoft.AspNetCore.Cors" Version="2.2.0" />

Any ideas what I am doing wrong?

Thank you!

[kphuanghk]

I copied your code with insignificant and small change to make the code run in my env, using dotnet5.

The CORS just works. You may review if your client makes call to the right endpoint.

let configureApp (app : IApplicationBuilder) =
    // Using IHostEnvironment
    let env = app.ApplicationServices.GetService<IHostEnvironment>()
    
    // Development State can be set via ASPNETCORE_ENVIRONMENT Environment Variable. Checking it here.
    let env_state = env.IsDevelopment()
    // logger.debug("configureApp()", [env_state], "Environment State, Development:")

In my case I do not need to refer to this

<PackageReference Include="Microsoft.AspNetCore.Cors" Version="2.2.0" />