Redirect service (302) in Azure, best possible approach?

I need to create a redirector that redirects user to an external domain while retaining the query params and one additional param.

e.g. When a user visits https://contoso.com/redirect?docId=123, it will redirect the user to https://contoso-v2.com/home?docId=123&token=xxxxxxx

Once user visits https://contoso.com/redirect?docId=123, this endpoint will process the info (from query params) and generate a token that needs to be appended in target URL.

What would be the most efficient and best way in Azure? Writing a simple Azure Web App or is there any better way?

You could use Azure Function with HttpTrigger Binding. With consumption plan the cost would be minimal (1 million invocations are free in pay-as-you-go plan).

using System.Net;

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

    var uri = req.RequestUri;
    var updatedUri = ReplaceHostInUri(uri, "contoso-v2.com");

    //return req.CreateResponse(HttpStatusCode.OK, "Original: " + uri + " Updated: " + updatedUri);
    return req.CreateResponse(HttpStatusCode.Found, updatedUri);
}

private static string ReplaceHostInUri(Uri uri, string newHostName) {
    var builder = new UriBuilder(uri);

    builder.Host = newHostName;
    //Do more trasformations e.g. modify path, add more query string vars

    return builder.Uri.ToString();
}