Bulk Uploading of Media Items to Cloud Storage Bucket Fails from 403

[neildaniels]

When uploading many photos to a post with the appengine-plugin enabled, the upload progress fails after a few images and I start getting "An error occurred in the upload. Please try again later." and "HTTP error." in the WordPress upload status pane.

In Safari, my console is showing errors like:
[Error] Failed to load resource: the server responded with a status of 403 (HTTP/2.0 403) (upload, line 0) for URLs like https://www.fomopop.com/_ah/upload/?post=118&action=edit/AMmfu6b8oibmt[…]

Then the WordPress admin page gives me a login overlay, making me re-authenticate into the admin page.

[neildaniels]

I never found a proper workaround for this. I would end up just uploading files directly to GCS and then import a list of GCS filenames as WordPress media items.

It's super janky and very manual, but it "works."

[wiz]

@neildaniels I fixed the bug, please take a look when you get a chance
#50