Authenticate with Azure AD using ASPNET Core 2 from behind Corporate Proxy - asp.net-core

Question

I have an ASPNET Core 2 application which I am trying to Authenticate with Azure AD using OpenId. I just have boilerplate code from selecting Single Organization Authentication in the ASPNET Core 2 templates, so no custom code. I followed the article here.
The app is not able to get metadata from the Azure AD application because of proxy. The same URL returns data if I just paste it in browser.
The error I get is:
HttpRequestException: Response status code does not indicate success: 407 (Proxy Authentication Required).
System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode()
IOException: IDX10804: Unable to retrieve document from: 'https://login.microsoftonline.com/my-tenant-id/.well-known/openid-configuration'.
Microsoft.IdentityModel.Protocols.HttpDocumentRetriever+d__8.MoveNext()
I have another ASPNET 4.5.2 application where I am able to perform authentication with the same Azure AD app as above after setting proxy in code like below:
System.Net.HttpWebRequest.DefaultWebProxy = new WebProxy
{
Address = new Uri("http://my-company-proxy:8080"),
Credentials = new NetworkCredential
{
UserName = "proxyusername",
Password = "proxypassword"
}
};
So Essentially my problem is to get past the Proxy Authentication in ASPNET Core 2.
I have tried Microsoft.AspNetCore.Proxy package. Its pretty much broken and doesn't work for me. Also I tried adding the Proxy entries in machine.config (which are actually not required for 4.5.2 app) but that doesn't work as well. I believe getting past a corporate proxy should be very trivial, but doesn't look like it so far.

Answer 1

Tratcher's comment pointed me in the right direction and I got it working, but just to help everyone with it, below is what you need to do:
builder.AddOpenIdConnect(options => options.BackchannelHttpHandler = new HttpClientHandler
{
UseProxy = true,
Proxy = new WebProxy
{
Credentials = new NetworkCredential
{
UserName = "myusername",
Password = "mypassword"
},
Address = new Uri("http://url:port")
}
});

Answer 2

In Full .net framework setting up a proxy is using a config setting
entry but to use an HTTP proxy in .net core ,you have to implement
IWebProxy interface.
Microsoft.AspNetCore.Proxy is proxy middleware which serves a different purpose (to setup reverse proxy) not as an http proxy .Refer this article for more details
To implement a webproxy in .net core,
public class MyHttpProxy : IWebProxy
{
public MyHttpProxy()
{
//here you can load it from your custom config settings
this.ProxyUri = new Uri(proxyUri);
}
public Uri ProxyUri { get; set; }
public ICredentials Credentials { get; set; }
public Uri GetProxy(Uri destination)
{
return this.ProxyUri;
}
public bool IsBypassed(Uri host)
{
//you can proxy all requests or implement bypass urls based on config settings
return false;
}
}
var config = new HttpClientHandler
{
UseProxy = true,
Proxy = new MyHttpProxy()
};
//then you can simply pass the config to HttpClient
var http = new HttpClient(config)
checkout https://msdn.microsoft.com/en-us/library/system.net.iwebproxy(v=vs.100).aspx