download.cs

[FunctionName("DownloadFile")]
public static IActionResult Run(
  [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "download/{fileId}")] HttpRequest req,
  string fileId,
  [Table("metadata", "{fileId}", "{fileId}", Connection = "TableConnectionString")] FileMetadata fileMetadata,
  [Table("ocrdata", Connection = "TableConnectionString")] CloudTable fileOcrDataTable,
  [Blob("files/{fileId}", FileAccess.Read, Connection = "StorageAccountConnectionString")] CloudBlockBlob fileBlob,
  ILogger log)
{
  if (!fileMetadata.ApprovedForDownload)
  {
    return new StatusCodeResult(403);
  }

  var readQuery = new TableQuery<OcrResult>();
  TableQuery.GenerateFilterCondition(nameof(OcrResult.PartitionKey), QueryComparisons.Equal, fileId);

  var ocrResults = fileOcrDataTable.ExecuteQuery(readQuery).ToList();
  return new OkObjectResult(new DownloadResponse
  {
    Metadata = ocrResults,
    FileId = fileId,
    DownloadUrl = GenerateSasUrlForFileDownload(fileBlob, fileId)
   });
}

static string GenerateSasUrlForFileDownload(CloudBlockBlob blob, string fileId)
{
  var policy = new SharedAccessBlobPolicy()
  {
    SharedAccessExpiryTime = DateTime.Now.AddHours(1),
    Permissions = SharedAccessBlobPermissions.Read
  };

  return blob.Uri + blob.GetSharedAccessSignature(policy);
}