HttpContext.Current.Request.Url giving 127.0.0.1

Question

I created a vanilla ASP.NET MVC AAD Authenticated application in Visual Studio 2017. It includes the following:

app.UseOpenIdConnectAuthentication(
                new OpenIdConnectAuthenticationOptions
                {
                    ClientId = clientId,
                    Authority = Authority,
                    PostLogoutRedirectUri = postLogoutRedirectUri,

                    Notifications = new OpenIdConnectAuthenticationNotifications()
                    {
                        // If there is a code in the OpenID Connect response, redeem it for an access token and refresh token, and store those away.
                        AuthorizationCodeReceived = (context) =>
                        {
                            var code = context.Code;
                            ClientCredential credential = new ClientCredential(clientId, appKey);
                            string signedInUserID = context.AuthenticationTicket.Identity.FindFirst(ClaimTypes.NameIdentifier).Value;
                            AuthenticationContext authContext = new AuthenticationContext(Authority, new ADALTokenCache(signedInUserID));
                            AuthenticationResult result = authContext.AcquireTokenByAuthorizationCode(
                            code, new Uri(HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Path)), credential, graphResourceId);
                            var graphUri = new Uri(AAD_GRAPH_URI);
                            var serviceRoot = new Uri(graphUri, tenantId);
                            this.aadClient = new ActiveDirectoryClient(serviceRoot, async () => await AcquireGraphAPIAccessToken(AAD_GRAPH_URI, authContext, credential));
                            return Task.FromResult(0);
                        }
                    }
});

For a while HttpContext.Current.Request.Url returns https://localhost:44345/ as is listed in the browser, and configured in Visual Studio for IIS Express.

However after a while it starts returning http://127.0.0.1/ instead! This results in the AzureAD auth returning the production URL instead of the localhost development URL.

I could hard code the development URL, but it is supposed to be dynamic so that it just works wherever I deploy it.

Why is IIS Express returning http://127.0.0.1/ instead of https://localhost:44345/ on my development box? And how do I get it to return the correct value. `