NET Core reverse proxy and authentication middleware

Question

I have .Net Core application hosted on an Azure app service, with a custom domain name set up in the Azure Front Door reverse proxy.

External authentication (Facebook) is implemented and works when I run the app locally and when I access the app on Azure directly using the [app_name].azurewebsites.net URL.

However, I get a server error when logging in via facebook when accessing the app either from my custom domain or via [app_name].azurefd.net.

The issue appears to be that, after auth, the user is redirected back to the app service domain (.azurewebsites.net/), instead of the custom domain.

I have configured forwarded headers in the application but that does not appear to have helped.

 services.Configure<ForwardedHeadersOptions>(options =>
            {
                options.ForwardedHeaders =
                    ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto | ForwardedHeaders.XForwardedHost | ForwardedHeaders.XForwardedHost;
                options.ForwardedHostHeaderName = "X-Original-Host";
                options.KnownNetworks.Clear();
                options.KnownProxies.Clear();
            });

My login code is the default generated by NET Core:

<form id="external-account" asp-page="./ExternalLogin" asp-route-returnUrl="@Model.ReturnUrl" method="post" class="form-horizontal">
                        <div>
                            <p>
                                @foreach (var provider in Model.ExternalLogins)
                                {
                                    <button type="submit" class="btn btn-primary" name="provider" value="@provider.Name" title="Log in using your @provider.DisplayName account">@provider.DisplayName</button>
                                }
                            </p>
                        </div>
                    </form>

There doesn't appear to be a Redirect_URI property I can set in the Facebook middleware options.

tldr: my .net core external auth middleware redirects to the azure domain instead of my custom domain even when app accessed from the custom domain. I have forwarded headers configured in NET Core.

Update: edited for clarity

Update2: Have also tried the following to no avail:

app.Use(async (context, next) =>
            {
                if (context.Request.Headers.Any(x => x.Value == "X-Original-Host") != false)
                {
                    var originalHost = context.Request.Headers.FirstOrDefault(x => x.Value == "X-Original-Host").Value;
                    context.Request.Headers.Add("Host", originalHost);
                }
                await next.Invoke();
            });

By specifying the correct redirect_uri in the login dialog URL you are sending the user to. — 04FS
– 04FS, Commented Jan 29, 2020 at 10:00
That should be a matter of some configuration setting or other. If the library you are using dynamically determines this based on a main app domain being set somewhere or something similar, then you might need to limit yourself to using this on one domain. — 04FS
– 04FS, Commented Jan 30, 2020 at 7:29

Victor · Accepted Answer · 2020-01-31 05:12:24Z

2

Same problem with redirects on Application Gateway per the following question: Redirect to absolute URL on timeout in ASP.NET Core 2.0 application

Thanks to Tratcher for his answer on that question. The solution was to add the following in the Configure method of Startup.cs:

app.Use((ctx, next) =>
{
    ctx.Request.Host = new HostString(options.Value.CustomDomain);
    return next();
});

answered Jan 31, 2020 at 5:12

Victor

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3 Comments

Leandro Bardelli Over a year ago

what is options? where do you get that?

user919532 Over a year ago

It is how they access their config values from appSettings for example. More here: pellerex.com/blog/asp-net-5-web-api-configuration-management

Rosdi Kasim Over a year ago

I added ASPNETCORE_FORWARDEDHEADERS_ENABLED in my Azure app service configuration and it works...

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