将会话请求添加到API调用

我不确定如何根据食品卫生说明将会话请求添加到API调用中。我已经复制了相关代码，并希望我能结识，但不确定将这一部分放在哪里。

参考：https：//api.ratings.food.gov.uk/help

需要添加到API调用中：Session.Request.Headers.Add（“ x-api-version”，2）;

部分代码：

   readonly string Baseurl = "https://api.ratings.food.gov.uk";
            public async Task<ActionResult> Index()
            {
                List<Authorities> AuthInfo = new List<Authorities>();
    
    
                using var client = new HttpClient
                { 
                //Passing service base url  
                BaseAddress = new Uri(Baseurl)
                };
    
                client.DefaultRequestHeaders.Clear();
                //Define request data format  
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                 
                ***//Session.Request.Headers.Add("x-api-version", 2);***
    
                //Sending request to find web api REST service resource GETRegions using HttpClient  
                HttpResponseMessage Res = await client.GetAsync("Authorities/basic");