A technique supports authentication of a server device (e.g., a web site). The technique involves supplying a user device (e.g., a client browser) with a user mechanism (e.g., a browser plug-in) which is constructed and arranged to dynamically generate user representations. The technique further involves receiving, at the server device, a request from the user device. The technique further involves providing a server representation to the user device from the server device in response to the request. The user device successfully authenticates the server device when a user representation dynamically generated by the user mechanism matches the server representation provided to the user device. However, the user device unsuccessfully authenticates the server device when the user representation dynamically generated by the user mechanism does not match the server representation provided to the user device.