.net Core - HTTPS with AWS Load Balancer and Elastic Beanstalk doesn't work

So I finally got this fixed. First, the Load Balancer has to be set to forward HTTPS 443 to HTTP 80 like this:

Then, ALL the code I've outlined in my question needs to be deleted (or not run in the AWS environment). I forgot to remove the services.Configure<MvcOptions>(options){} lines of code initially and I believe that was what was causing the error.

Then I followed this blog to handle the X-Forwarded-Proto header. I put all the code in one extension file:

public static class RedirectToProxiedHttpsExtensions
{
    public static RewriteOptions AddRedirectToProxiedHttps(this RewriteOptions options)
    {
        options.Rules.Add(new RedirectToProxiedHttpsRule());
        return options;
    }
}

public class RedirectToProxiedHttpsRule : IRule
{
    public virtual void ApplyRule(RewriteContext context)
    {
        var request = context.HttpContext.Request;

        // #1) Did this request start off as HTTP?
        string reqProtocol;
        if (request.Headers.ContainsKey("X-Forwarded-Proto"))
        {
            reqProtocol = request.Headers["X-Forwarded-Proto"][0];
        }
        else
        {
            reqProtocol = (request.IsHttps ? "https" : "http");
        }


        // #2) If so, redirect to HTTPS equivalent
        if (reqProtocol != "https")
        {
            var newUrl = new StringBuilder()
                .Append("https://").Append(request.Host)
                .Append(request.PathBase).Append(request.Path)
                .Append(request.QueryString);

            context.HttpContext.Response.Redirect(newUrl.ToString(), true);
        }
    }
}

Finally, I call this code in Startup.cs:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    ...
    var options = new RewriteOptions()
        .AddRedirectToProxiedHttps()
        .AddRedirect("(.*)/$", "$1");  // remove trailing slash
    app.UseRewriter(options);
    ... 
}

After all that it finally worked!

According to this AWS docs you must analyze X-Forwarded-Proto header and response with redirects only when it is http (not https).

Current RedirectToHttpsRule from Microsoft.AspNetCore.Rewrite package does not analyze this. You need to implement your own IRule.