Session state is typically passed to the browser in the Set-Cookie header of an HTTP response. The browser will then return the same information back in the Cookie header.
Set-Cookie
Cookie
Headers ▼ General Remote Address: 121.232.112.200:443 Request Method: GET Status Code: 200 OK ▶ Request Headers ▼ Response Headers Set-Cookie: session_id=142983010 Set-Cookie: user_id=3829