Google Authenticator Auth

A simple class to work with Google Authenticator from ruby. Can
generate a secret key along with qrcode url/image and generate
one time passwords for a secret key.

See Also: http://code.google.com/p/google-authenticator/

ga = GoogleAuthenticator.new
ga.secret_key # => "NINWS2QUIQD2LA2Z" 
ga.qrcode_url('user@domain.com') # => "otpauth://totp/user@domain.com?secret=NINWS2QUIQD2LA2Z"
ga.qrcode_image_url('user@domain.com') # => "https://chart.googleapis.com/chart?chs=350x350&cht=qr&choe=UTF-8&chl=otpauth://totp/user@domain.com?secret=NINWS2QUIQD2LA2Z"

ga = GoogleAuthenticator.new('NINWS2QUIQD2LA2Z')
ga.key_valid?(key) # => true or false

ga = GoogleAuthenticator.new('NINWS2QUIQD2LA2Z')
ga.get_keys # => [Previous, Current, Next]