Testing my own Forge app in dev mode on my Jira dev instance and it is asking me to authorize the app:
Clicking Allow access leads to a 431 HTTP error:
Closing the tab changes the message to:
This may be a Chrome issue (Version 92.0.4515.107 (x86_64)) because it seems to work in Firefox. I cannot remember exactly what I did that caused the app to request permissions again but I think it came up after I added permission for images:
permissions: external: images: - '*.giphy.com'
Happy to provide more details if necessary.