Django - upload a file to the cloud (Azure blob storage) with progress bar

I'm following this tutorial to add a progress bar when I'm uploading a file in Django, using ajax. When I'm uploading the file to a folder using the upload_to option everything works fine. But when I'm uploading the file to Azure using the storage option - It doesn't work. i.e. when this is my model:

class UploadFile(models.Model):
    title = models.CharField(max_length=50)
    file=models.FileField(upload_to='files/media/pre')

It works perfect, but when this is my model:

from myAzure import AzureMediaStorage as AMS
class UploadFile(models.Model):
    title = models.CharField(max_length=50)
    file = models.FileField(storage=AMS)

It gets stuck and not progressing. (AMS is defined in myAzure.py by):

from storages.backends.azure_storage import AzureStorage

class AzureMediaStorage(AzureStorage):
    account_name = '<myAccountName>'
    account_key = '<myAccountKey>'
    azure_container = 'media'
    expiration_secs = None

How can I make it work?

EDIT: If it was not clear:

• my problem is not to upload to Azure, but to show progress bar.
• From security reasons I do not want to upload the file from the browser and to use CORS and SAS but from my backend.

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