Jenkins 2.218 and earlier, LTS 2.204.1 and earlier exposed session identifiers on a user's detail object in the whoAmI diagnostic page.
{
"versions": [
{
"introduced": "0"
},
{
"last_affected": "2.204.1"
},
{
"introduced": "0"
},
{
"last_affected": "2.218"
}
]
}