Azure Function - Blob Storage to SFTP

Question

I am working on a data pipeline on Azure that in the end produces a file on a Blob Container. This file needs to be then uploaded on a SFTP on a given schedule. I am using Azure Data Factory for the pipeline scheduling, but ADF doesn't yet support SFTP as a sink. The following code is an attempt to use Azure Functions to solve this part of the pipeline. This Azure Function would then be called from within ADF, which is why I am not using a Blob Trigger but an HTTP Trigger. It is mostly inspired by https://github.com/GinSiuCheng/azure-sample-function-sftp-upload/blob/master/azure-sample-function-sftp-upload/sftpUpload.cs

I came up with the following code, and am struggling to understand the Stream aspect. The code produces a file on the SFTP but it is empty.

namespace Company.Function
{

    public static class HttpTriggerSFTP
    {

        private static CloudBlockBlob cloudBlockBlobToTransfer;
        private static System.IO.Stream fileStream ;
        [FunctionName("HttpTriggerSFTP")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            log.LogInformation("C# HTTP trigger function processed a request.");

            string name = req.Query["name"];

            // Storage Account Parameters
            string storageAccountKey =  req.Headers["storageAccountKey"];
            string storageAccountContainer =  req.Headers["storageAccountContainer"];
            string storageAccountPath =  req.Headers["storageAccountPath"];
            string sourceFileName =  req.Headers["sourceFileName"];
            string storageConnectionString = req.Headers["storageConnectionString"];
            string sourceFileAbsolutePath = storageAccountPath + '/' + sourceFileName;
            log.LogInformation(sourceFileAbsolutePath);

            // SFTP Parameters
            string sftpAddress =  req.Headers["sftpAddress"];
            string sftpPort =  req.Headers["sftpPort"];
            string sftpUsername =  req.Headers["sftpUsername"];
            string sftpPassword =  req.Headers["sftpPassword"];
            string sftpPath =  req.Headers["sftpPath"];
            string targetFileName =  req.Headers["targetFileName"];
            var memoryStream = new MemoryStream();

            CloudStorageAccount storageAccount; 
            if (CloudStorageAccount.TryParse(storageConnectionString, out storageAccount))
            {

                // If the connection string is valid, proceed with operations against Blob storage here.
                CloudBlobClient cloudBlobClient = storageAccount.CreateCloudBlobClient();

                // Create a container called 'quickstartblobs' and append a GUID value to it to make the name unique.
                CloudBlobContainer cloudBlobContainer = cloudBlobClient.GetContainerReference(storageAccountContainer);

                log.LogInformation("looking for file",sourceFileAbsolutePath);
                cloudBlockBlobToTransfer = cloudBlobContainer.GetBlockBlobReference(sourceFileAbsolutePath);
                await cloudBlockBlobToTransfer.DownloadToStreamAsync(memoryStream);
                log.LogInformation("Blob connection Ok");

            }

            var methods = new List<AuthenticationMethod>();
            methods.Add(new PasswordAuthenticationMethod(sftpUsername, sftpPassword));

            // Connect to SFTP Server and Upload file 
            Renci.SshNet.ConnectionInfo con = new Renci.SshNet.ConnectionInfo(sftpAddress, sftpPort, new PasswordAuthenticationMethod(sftpUsername, sftpPassword));
            using (var client = new SftpClient(con) )
            {
                client.Connect();                

                log.LogInformation("About to upload to sftp");
                client.UploadFile(memoryStream, $"/{sftpPath}/{targetFileName}");

                var files = client.ListDirectory(sftpPath);
                foreach (var file in files)
                {
                    log.LogInformation(file.Name);
                }
                client.Disconnect();
            }



        }
    }
}

I'd like to understand why my stream is empty ? How can I ensure that I am loading data in it ?

I am also planning on using Key Vault to store credentials instead of putting it in headers.

Thanks for your time.