The authentication mechanism most widely deployed and used by Internet application protocols is the transmission of clear-text passwords over a channel protected by Transport Layer Security (TLS). There are some significant security concerns with that mechanism, which could be addressed by the use of a challenge response authentication mechanism protected by TLS. Unfortunately, the HTTP Digest challenge response mechanism presently on the standards track failed widespread deployment, and have had success only in limited use. This specification describes a family of HTTP authentication mechanisms called the Salted Challenge Response Authentication Mechanism (SCRAM), which addresses security concerns with HTTP Digest and meets the deployability requirements. When used in combination with TLS or an equivalent security layer, a mechanism from this family could improve the status-quo for HTTP authentication.