Sticky session
A setting that keeps the same exit address for a fixed period, so a multi-step flow appears to come from one user.
A sticky session holds one exit address for a defined duration instead of rotating. Typical windows run from one minute to roughly thirty, depending on the provider.
#Why it exists
Many tasks are not a single request. Logging in, adding to a basket, paging through results, or completing a form all involve several requests that a server expects to originate from one client. If the address changes halfway through, the session looks implausible and may be discarded or challenged.
#How it is usually requested
Most providers accept a session identifier inside the proxy username, for example a field such as session-abc123. Requests carrying the same identifier are routed through the same address until the window expires. The exact syntax differs by provider.
#What it does not guarantee
Stickiness is best-effort. If the underlying address leaves the pool — a residential peer disconnects, for example — the session ends early and you receive a different address. Code that assumes a stable address for the full window will eventually be surprised, so detect the change rather than assume it cannot happen.