How do I add a header to a web reference?

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.NET4.5

I have an old .net Framework assembly project that uses a SOAP Web Reference. These references were created via right clicking on references - Add Service Reference - Advanced - Add Web Reference.

The SOAP Web Service is now requiring oAuth authentication. I'm able to retrieve the Bearer Token but I don't know how to add it to a Header via a Web Reference.

If I wasn't going through the Web Reference I would do it like this:

var http = new System.Net.Http.HttpClient();
http.DefaultRequestHeaders.Add("Authorization", "Bearer " + Globals.BearerToken);

Does anyone know how I would do the equivalent through the Web Reference.

I appreciate the help.

What I have tried:

Couldn't find anything online that addressed this specifically.