Function.cs

using System.Net;
using System.Text.Json;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;

namespace Microsoft.PWABuilder.ManifestCreator;

public class Function
{
    private readonly ILogger _logger;

    public Function(ILoggerFactory loggerFactory)
    {
        _logger = loggerFactory.CreateLogger<Function>();
    }

    [Function("Create")]
    public async Task<HttpResponseData> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData req)
    {
        var queryString = System.Web.HttpUtility.ParseQueryString(req.Url.Query);

        // Grab the URL. Prepend https:// to it if necessary.
        var url = queryString["url"];
        if (url != null && !url.StartsWith("http://", StringComparison.OrdinalIgnoreCase) && !url.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
        {
            url = $"https://{url}";
        }

        if (!Uri.TryCreate(url, UriKind.Absolute, out var uri))
        {
            _logger.LogError("Bad request. Expected query string to be absolute URL. Actual value {val}", url);
            var errorResponse = req.CreateResponse(HttpStatusCode.BadRequest);
            errorResponse.WriteString("URI must be validate, absolute URI");
            return errorResponse;
        }

        var manifestService = new ManifestService(uri, _logger);
        var manifest = await manifestService.CreateManifest();
        var okResponse = req.CreateResponse(HttpStatusCode.OK);
        await okResponse.WriteStringAsync(JsonSerializer.Serialize(manifest, new JsonSerializerOptions { DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.WhenWritingNull }));
        return okResponse;
    }
}