Technology related to multi-device authentication is disclosed. In one example, a method can include receiving a request from a requesting client device to access a secured server. A command can be sent to an authenticating device to capture environmental information in proximity to the authenticating device. The captured environmental information can be used to verify the requesting client device and the authenticating device are near each other. The received request can be forwarded to the secured server in response to verifying the requesting client device and the authenticating device are near each other.