Does F5 extract Authorization header from C# HttpWebRequest ?

A web application written in C# sends request to downstream. F5 provides the auth services.

C# web app -> F5 -> Downstream App

Downstream App expects Basic Auth to authn/authz.

The credentials are set similar to below.

Set with System.net.NetworkCredentials and web request to downstream sent via HttpWebRequest.

There is NO 'Authorization' header sent to downstream App.

But F5 logs show 'Authorization' header.

Authorization = Basic blahblah

From where did F5 get this Authorization header? 😐

//Create a HTTP Web Request Instance
            var httpWebRequest = (HttpWebRequest) WebRequest.Create(uri);
            //Set the request type to Get
            httpWebRequest.Method = "GET";
            //Set Credential
            String UserId = "someUserId";
            String UserPassword = "somePassword";
            String DomainName = "SomeDomain";
            NetworkCredential networkCredential=new NetworkCredential(UserId,UserPassword,DomainName);
           

Thank you for your help!