Mobile device, client device and server associated with client-server authentication are described. In embodiments, the mobile device may comprise a camera and a token extractor. The token extractor may be coupled to the camera and configured to analyze an image, captured by the camera. The captured image may contain a barcode and may be displayed on a client device in response to a request of a server for access to a resource. The barcode may contain a token, which may be extracted by the token extractor to be used to gain access to a resource requested from a server. Other embodiments may be described and/or claimed.