KIP-368: Allow SASL Connections to Periodically Re-Authenticate
The adoption of KIP-255: OAuth Authentication via SASL/OAUTHBEARER in release 2.0.0 creates the possibility of using information in the bearer token to make authorization decisions. Unfortunately, however, Kafka connections are long-lived, so there is no ability to change the bearer token associated with a particular connection. Allowing SASL connections to periodically re-authenticate would resolve this. In addition to this motivation there are two others that are security-related. First, to eliminate access to Kafka the current requirement is to remove all authorizations (i.e. remove all ACLs). This is necessary because of the long-lived nature of the connections. It is operationally simpler to shut off access at the point of authentication, and with the release of KIP-86: Configurable SASL Callback Handlers it is going to become more and more likely that installations will authenticate users against external directories (e.g. via LDAP). The ability to stop Kafka access by simply disabling an account in an LDAP directory (for example) is desirable. The second motivating factor for re-authentication related to security is that the use of short-lived tokens is a common OAuth security recommendation, but issuing a short-lived token to a Kafka client (or a broker when OAUTHBEARER is the inter-broker protocol) currently has no benefit because once a client is connected to a broker the client is never challenged again and the connection may remain intact beyond the token expiration time (and may remain intact indefinitely under perfect circumstances). This KIP proposes adding the ability for clients (and brokers when OAUTHBEARER is the inter-broker protocol) to re-authenticate their connections to brokers and have the new bearer token appear on their session rather than the old one.