Problem

I need to do some validation like full hard reboot of device and safe mode but I have applied the changes you made in your fix commit and it will authenticate, but I am getting 400's when Cura is trying to upload to Octoprint. I have tried refreshing the API Token so far:
From Cura Log:

2025-01-31 23:52:13,072 - ERROR - [MainThread] OctoPrintPlugin.OctoPrintOutputDevice._onUploadFinished [1608]: OctoPrintOutputDevice got an 400 error uploading to https://{redacted}:443/api/files/local
2025-01-31 23:52:13,073 - ERROR - [MainThread] OctoPrintPlugin.OctoPrintOutputDevice._onUploadFinished [1614]: OctoPrint responded with an unknown error

Octoprint (via Octo4a) Tornado Log:

2025-01-31 13:22:12 - tornado.access - WARNING - 400 POST /api/files/local (192.168.1.215) 618.92ms

Other Tornado Log 400's from other integration:

2025-01-31 10:21:34 - tornado.access - WARNING - 400 POST /api/plugin/octoapp (192.168.1.215) 95.24ms
2025-01-31 10:23:54 - tornado.access - WARNING - 400 POST /api/plugin/octoapp (192.168.1.215) 19.00ms
2025-01-31 10:26:10 - tornado.access - WARNING - 400 POST /api/plugin/octoapp (192.168.1.215) 37.67ms

One thing I will try that should be an easy test is going via local direct IP, both octoapp and cura are going via my public domain 🤔
It shouldn't make a difference because the .215 proxy is in the list of trusted proxies but who knows 🤷

Edit: Can confirm same issue over local IP instead of public domain:

localhost:~$ tail /mnt/external/.octoprint/logs/tornado.log | grep " 400 "
2025-01-31 13:29:41 - tornado.access - WARNING - 400 POST /api/login (192.168.2.91) 8.03ms
2025-01-31 13:29:41 - tornado.access - WARNING - 400 POST /api/login (192.168.2.91) 10.24ms
2025-01-31 13:29:42 - tornado.access - WARNING - 400 POST /api/login (192.168.2.91) 26.91ms
2025-01-31 13:29:42 - tornado.access - WARNING - 400 POST /api/login (192.168.2.91) 7.65ms

Edit 2: Originally I didn't see this but extra info from Octoprint log, these are absolutely spamming for these failed connections:

2025-01-31 13:28:29,401 - octoprint.server.util.sockjs - INFO - New connection from client: 192.168.1.215
2025-01-31 13:28:30,311 - octoprint.server.util.sockjs - WARNING - Unknown user/session combo: null:null
...
2025-01-31 13:30:00,208 - octoprint.server.util.sockjs - INFO - New connection from client: 192.168.2.91
2025-01-31 13:30:00,307 - octoprint.server.util.sockjs - WARNING - Unknown user/session combo: null:null

Originally posted by @XxInvictus in #5098

Can confirm this on a local checkout of staging/maintenance, so there's still an issue here that needs solving.

Solution

Currently unsure, investigating.