14. The non-transitory machine-readable storage medium of claim 12 , the instructions, when executed by the computing device, cause the computing device to perform a method further comprising: performing speech recognition on the second audio signal to extract spoken words that correspond to the second text-phrase; comparing the spoken words against the second text-phrase to generate a first confidence score; extracting features from the second audio signal; comparing the features against the text-phrase to generate a second confidence score; and saving the text-phrase indexed based on an identity indicated in the second request if the first and second confidence scores exceed a threshold.
12. The non-transitory machine-readable storage medium of claim 9 , the instructions further comprising: receiving a second request from a second end-user system for registration; generating a second text-phrase; transmitting the second text-phrase to the second end-user system; and receiving a second audio signal from the second end-user system that corresponds to the second text-phrase.