Usability of web authentication systems refers to the efficiency and user acceptance of online authentication systems. Examples of web authentication systems are passwords, federated identity systems (e.g. Google oAuth 2.0, Facebook connect, Mozilla persona), email-based single sign-on (SSO) systems (e.g. SAW, Hatchet), QR code-based systems (e.g. Snap2Pass, WebTicket) or any other system used to authenticate a user's identity on the web. Even though the usability of web authentication systems should be a key consideration in selecting a system, very few web authentication systems (other than passwords) have been subjected to formal usability studies or analysis. Usability and users A web authentication system needs to be as usable as possible whilst not compromising the security that it needs to ensure. The system needs to restrict access by malicious users whilst allowing access to authorised users. If the authentication system does not have sufficient security, malicious users could easily gain access to the system. On the other hand, if the authentication system is too complicated and restrictive, an authorised user would not be able to (or want to) use it. Strong security is achievable in any system, but even the most secure authentication system can be undermined by the users of the system, often referred to as the "weak links" in computer security. Users tend to inadvertently increase or decrease security of a system. If a system is not usable, security could suffer as users will try to minimize the effort required to provide input for authentication, such as writing down their passwords on paper. A more usable system could prevent this from happening. Users are more likely to oblige to authentication requests from systems that are important (e.g. online banking), as opposed to less important systems (e.g. a forum that the user visits infrequently) where these mechanisms might just be ignored. Users accept the security measures only up to a certain point before becoming annoyed by complicated authentication mechanisms. An important factor in the usability of a web authentication system is thus the convenience factor for the user around it. Usability and web applications The preferred web authentication system for web applications is the password, despite its poor usability and several security concerns. This widely used system usually contains mechanisms that were intended to increase security (e.g. requiring users to have high entropy passwords) but lead to password systems being less usable and inadvertently less secure. This is because users find