Abstract: An authentication token one side of which features an array of solar cells, of a very thin and flexible type, whereas the opposite side features a display device. The method consists in encoding into a sequence of bright images, interlaced with less bright ones, the code sent by the server. By placing the token in front of the portion of the screen displaying said encoding sequence, the light collected by the array of solar cells it is sufficient to generate the energy required for supplying the token's microprocessor, while the variation in brightness are decoded as to reconstruct the digital word representing the code sent by the server. Said code is then processed by the microprocessor to generate a One Time Password, OTP, then displayed on the display device. The user would then enter said OTP on the login page.