ASP.NET Core form ignoring asp-controller

Question

I'm working on an ASP.NET Core application. Part of it is an image gallery which allows the user to upload images. On localhost this works as expected, but when I deploy (AWS Lambda with API Gateway) the upload button is missing the asp-controller attribute.

I have a GalleryController.cs with two methods:

 public async Task<IActionResult> Index()
 {
      // Pulls images from aws S3, adds them to a list and passes them to then returns View();
 }

 [HttpPost("Upload")]
 public async Task<IActionResult> Upload(List<IFormFile> files)
 {
      // For each iformFile in Files, create a thumbnail in memory then upload both the original and thumbnail to aws s3 bucket
      return RedirectToAction("Index");
 }

The routing configuration in my startup.cs has been left default from the boilerplate:

app.UseEndpoints(endpoints =>
{
    endpoints.MapControllerRoute(
        name: "default",
        pattern: "{controller=Home}/{action=Index}/{id?}");
});

The folder structure for my Views is as follows:

├── Views
│   ├── Gallery
│   │   ├── _GalleryPartial.cshtml
│   │   ├── Index.cshtml
│   │   └── _UploadPartial.cshtml
│   ├── Home
│   │   └── Index.cshtml

_UploadPartial.cshtml looks like this:

<div class="container">
    <div class="col-md-12">
        <form method="post" enctype="multipart/form-data" asp-controller="Gallery" asp-action="Upload">
            <div class="form-group">
                <div class="col-md-12">
                    <div class="col-md-6">
                        <input class="form-control-file" type="file" name="files" multiple />
                    </div>
                    <div class="col-md-6">
                        <input class="form-control-file" type="submit" value="Upload" />
                    </div>
                </div>
            </div>
        </form>
    </div>
</div>
<hr>

As you can see I have asp-controller="Gallery" and asp-action="Upload", but when I inspect the form after deploying it to lambda it seems to be ignoring the controller tag.

Looks like I don't have enough points to embed an image therefore SO created a link

edit As per request, here is the contents of Gallery/index.cshtml

@model Dictionary<string, string>
    
@{
    ViewData["Title"] = "News page";
}
<center>
    @await Html.PartialAsync("_uploadPartial")


    @await Html.PartialAsync("_galleryPartial")
</center>

And the contents of my startup.cs:

using Amazon.S3;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Authentication.OpenIdConnect;
using Redacted.Helpers;

namespace Redacted;

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews().AddRazorRuntimeCompilation();

        services.AddAWSService<IAmazonS3>();
        services.AddTransient<ImageHelper>();


        services.AddRazorPages();
        services.AddMvcCore();
        services.AddAuthentication(options =>
        {
            options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            options.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            options.DefaultChallengeScheme = OpenIdConnectDefaults.AuthenticationScheme;
        })
        .AddCookie()
        .AddOpenIdConnect(options =>
        {
            // Signin:
            options.ResponseType = Environment.GetEnvironmentVariable("ResponseType");
            options.MetadataAddress = Environment.GetEnvironmentVariable("MetadataAddress");
            options.ClientId = Environment.GetEnvironmentVariable("ClientId");
            options.ClientSecret = Environment.GetEnvironmentVariable("ClientSecret");
            // Signout
            options.Events = new OpenIdConnectEvents()
            {
                OnRedirectToIdentityProviderForSignOut = OnRedirectToIdentityProviderForSignOut
            };
        });

        services.AddAuthorization(options =>
        {
            options.AddPolicy("Admins", policy => policy.RequireAssertion(context => context.User.HasClaim(c => c.Type == "cognito:groups" && c.Value == "admins")));
            options.AddPolicy("Users", policy => policy.RequireAssertion(context => context.User.HasClaim(c => c.Type == "cognito:groups" && c.Value == "users" || c.Value == "admins")));
        });
    }


    // 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
        {
            app.UseExceptionHandler("/Error");
            // 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.UseStaticFiles();

        app.UseRouting();

        app.UseAuthentication();
        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller=Home}/{action=Index}/{id?}");
        });



    }

    private Task OnRedirectToIdentityProviderForSignOut(RedirectContext context)
    {


        context.ProtocolMessage.Scope = "openid";
        context.ProtocolMessage.ResponseType = "code";

        var cognitoDomain = Environment.GetEnvironmentVariable("CognitoDomain");
        var clientId = Environment.GetEnvironmentVariable("ClientId");
        var logoutUrl = Environment.GetEnvironmentVariable("LogoutUri");

        context.ProtocolMessage.IssuerAddress = $"{cognitoDomain}/logout?client_id={clientId}&logout_uri={logoutUrl}&redirect_uri={logoutUrl}";

        // delete cookies
        context.Properties.Items.Remove(CookieAuthenticationDefaults.AuthenticationScheme);
        // close openid session
        context.Properties.Items.Remove(OpenIdConnectDefaults.AuthenticationScheme);

        return Task.CompletedTask;
    }
}

Answer 1

After some time debugging I discovered the problem was with the infrastructure itsself. As i'm using API Gateway to route traffic to my lambda I was missing routes for POST. Simply adding a POST route method to /{proxy+} under api gateway/routes in the aws console OR using a terraform resource block similar to this:

resource "aws_apigatewayv2_route" "get_route" {
  api_id    = aws_apigatewayv2_api.lambda.id

  route_key = "GET /{proxy+}"
  target    = "integrations/${aws_apigatewayv2_integration.proxy_integration.id}"
}