Just a note for myself for the NEXT time this happens.
If Confluence starts returning an error saying "400 Bad Request - Request Header Or Cookie Too Large" then the cause is that something has gotten borked with the cookie that the browser has for Confluence. The fix is to delete the Confluence cookie (then log in again). Deleting cookies for a specific site is surprisingly hard. For Chrome, here is the process:
- From the triple-dot menu near the right-top, select "Settings".
- Scroll to the bottom and select "Advanced".
- Search in the page for "Content settings" (and NOT for "cookies").
- Select "Content Settings".
- Then select "Cookies".
- Then select "See all cookies and site data".
- Now you have a list of sites and can delete cookie data for any site you like.
You might think they would make this easier.