1. A computer-implemented method, comprising: at a server having one or more processors and memory storing programs executed by the one or more processors: receiving a login request from a mobile device, the login request including video data and audio data; extracting a group of facial features from the video data; extracting a group of audio features from the audio data and recognizing a sequence of words in the audio data; identifying, in a user account database, a first user account whose respective facial features match the group of facial features according to first predefined criteria; identifying, in the user account database, a second user account whose respective audio features match the group of audio features according to second predefined criteria; if the first user account is the same as the second user account: comparing the recognized sequence of words with a predefined sequence of words associated with the first user account; authenticating the login request if the recognized sequence of words matches the predefined sequence of words according to third predefined criteria; and if the recognized sequence of words does not match the predefined sequence of words according to the third predefined criteria, returning a first response to the mobile device, indicative of the denial of the login request; and if the first user account is different from the second user account: returning a second response to the mobile device, indicative of the denial of the login request.