HTTP Authentication
HTTP Authentication is the built in mechanism of the HTTP 1.x protocol for requiring a valid username or password to gain access to web resources. This mechanism can be initiated by either a CGI script or by the web server itself.
There are currently 2 modes of authentication built into the HTTP 1.1 protocol, termed "Basic" and "Digest" Access Authentication.
Basic Authentication transmits the username-password pair in an unencrypted form from the browser to the server and in such should not be used for sensitive logins unless operating over an encrypted medium such as SSL.
Digest Authentication sends the server a one way hash of the username-password pair calculated with a time sensitive, server supplied salt value.