http://blog.tyang.org/2016/10/13/making-powershell-based-azure-functions-to-produce-html-outputs/

HTTPTriggerProxy.csx

using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using System.IO;
using System.Text;

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    log.Info($"C# HTTP trigger proxy function processed a request. RequestUri={req.RequestUri}");

    // parse query parameter
    string requesturl = req.GetQueryNameValuePairs()
        .FirstOrDefault(q => string.Compare(q.Key, "requesturl", true) == 0)
        .Value;
    log.Info($"C# HTTP trigger proxy function is trying to get response from {requesturl}");

    Encoding outputencoding = Encoding.GetEncoding("ASCII");
    var ProxyResponse = new HttpResponseMessage();
    HttpStatusCode statuscode = new HttpStatusCode();
    
    if (requesturl == null)
    {
        statuscode = HttpStatusCode.BadRequest;
        StringContent errorcontent =new StringContent("Please pass a web request url on the query string or in the request body", outputencoding); 
        ProxyResponse = req.CreateResponse(statuscode, errorcontent);
        ProxyResponse.Content.Headers.ContentType = new MediaTypeHeaderValue("text/html");
        ProxyResponse.Content = errorcontent;
    } else {
        HttpClient client = new HttpClient();
        HttpResponseMessage response = await client.GetAsync(requesturl);
        ProxyResponse = response;
        ProxyResponse.Content.Headers.ContentType = new MediaTypeHeaderValue("text/html");
    }
    return ProxyResponse;
}