Techniques are disclosed relating to communication of authentication information in an access control system. Authentication information is transmitted to an electronic locking device configured to restrict access to an entry point of the access control system. A smart device comprises a light-emitting diode (LED) and a wireless networking radio for exchanging access control information with a remote server. The smart device may receive information from the remote server that configures the LED to present authentication information as an optical signal. The electronic locking device may comprise a photodetector arranged to receive the optical signal. According to various embodiments, the smart device may comprise a user interface display. Presentation of the authentication information may include rendering a webpage comprising a dynamic visual feature that changes visual content appearing on the user interface display so as to convey the authentication information as the optical signal emitted by the user interface display.