431 Request Header Fields Too Large
When a client sends a HTTP request with HTTP headers that are too big, a server
can use 431 Request Headers Fields Too Large in response.
This response can be used if either the total size of all headers exceeded some limit, or if there are individual headers that are too big.
If a client sees a 431, it could hypothetically remove some headers and try
again. The most obvious candidate for this could be removing cookies.
Example
HTTP/1.1 431 Request Headers Too Large
Content-Type text/html
<h1>Too many cookies! Try to reduce your cookie footprint.</h1>
References
- RFC6585, Section 5 - 431 Request Headers Fields Too Large