Which URL to use for <img src=""> to preview an Attachment image on web page outside of Asana?

I use Asana Web API to get information and show it in my Web application.
I would like to show an image from Asana Attachment.
Until some point back in time I used permanent_url for and this worked.
Now the image is not shown.
Fiddler shows Html Status code “303 See Other”
Direct insertion of permanent_url to the browser address bar redirects to view_url (wich is temporary).

Which recommendation do we have to show an attachment image knowing permanent_url?