ソースコード

using System;
using System.Collections;
using System.Text;
using UnityEngine;

public class Example : MonoBehaviour
{
    private IEnumerator Start()
    {
        var url             = "【URL】";
        var form            = new WWWForm();
        var headers         = form.headers;
        var s               = "【ユーザー名】:【パスワード】";
        var inArray         = Encoding.UTF8.GetBytes( s );
        var basicAuth       = Convert.ToBase64String( inArray );
        var authorization   = "Basic " + basicAuth;

        headers[ "Authorization" ] = authorization;
        
        var www = new WWW( url, null, headers );
        yield return www;

        // ...
    }
}

参考サイト様