authenticates the user. A web application can generate a unique personal identification number (PIN) that the user can input into the desktop client, the desktop client, in turn, uses that code to authenticate itself to the web application. This form of authentication is particularly useful in web applications that do not have an internal username/password store but instead use SAML for authentication. Since SAML only works within the browser, a desktop-based web application client cannot successfully authenticate using SAML. Instead, the client application can use the one-time authorization code (OTAC) to authenticate itself to the web application. In addition, it is possible to use the OAuth authorization framework when a third party application needs to obtain limited access to an HTTP service. Post It is possible to send OTACs to a user via post or registered mail. When a user requests an OTAC, the service provider sends it via post or registered mail and then the user can use it for authentication. For example, in the UK, some banks send their OTAC for Internet banking authorization via post or registered mail. Expansion Quantum cryptography, which is based on the uncertainty principle is one of the ideal methods to produce an OTAC. Moreover, it has been discussed and used not only using an enciphered code for authentication but also using graphical one time PIN authentication such as QR code which provides decentralized access control technique with anonymous authentication. See also Google Authenticator FreeOTP Initiative For Open Authentication Key-agreement protocol KYPS One-time pad OPIE Authentication System OTPW Personal identification number Public Key Infrastructure QR Code S/KEY Security token Time-based One-time Password algorithm Two-factor authentication References Password authentication Computer access control