Token binding is a security control that ties a token, artifact, or credential to a specific session, user, device, or workflow. Instead of treating the token as portable, the system checks that it is being presented in the exact context where it was issued. If the context does not match, the token is rejected.
This matters because replay attacks often succeed when an attacker copies a valid token and reuses it elsewhere. In web systems, that can mean hijacked sessions; in AI APIs, it can mean replaying hidden reasoning artifacts across conversations or tenants. Proper binding helps stop state confusion, cross-session reuse, and unauthorized access to logs or cached protocol data. Defenders use it alongside short lifetimes, signature checks, nonce values, and strict session validation. If token binding is weak or absent, any leaked token can become a bridge from a narrow flaw to broader compromise.