Two-factor authentication example with Vaadin
tl:dr This example shows how to make a Vaadin application work with Google Authenticator.
An example using two-factor authentication (also known as two-step verification) in a Vaadin application. This allows the application to add an additional layer of security, by requiring a one-time "TOTP" password to be entered.
TOTP RFC: http://tools.ietf.org/html/rfc6238
TOTP java library: https://github.com/wstrange/GoogleAuth (there are other implementation on GitHub, and a messy reference implementation in the RFC)
QRCode add-on: http://vaadin.com/addon/qrcode