http.cookies: parser accepts key characters that Morsel.set then rejects

Bug report

Bug description:

SimpleCookie.load() extracts cookie names using _LegalKeyChars, which deliberately admits characters RFC 6265 forbids in a token — the comment above it cites MSIE non-compliance as the reason. Morsel.set() then validates with _is_legal_key, built from _LegalChars, which excludes them. Twelve separator characters differ, so any Set-Cookie whose name contains one raises CookieError even though the module's own parser accepted it.

Encountered in the wild: F5 BIG-IP load balancers emit a persistence cookie named for the partition path, /Common/.app/--pool. Browsers accept this...

from http.cookies import SimpleCookie
SimpleCookie('/a/b=1')      # also a@b=1, a,b=1, a(b)=1

CPython versions tested on:

3.14

Operating systems tested on:

Linux

この issue では SimpleCookie.load()、Morsel.set()、_LegalKeyChars、_is_legal_key、_LegalChars が挙げられています。まず、これらの parser および validation の経路を追跡し、一覧にある cookie 名を再現してください。受け入れられる名前の動作に一貫性があり、例で CookieError が発生しなくなり、その不一致に対する regression coverage があれば完了です。