Yes yes yes. Here it is...If you ever wanted to know how the "mouth from the south" sounds like LIve...just watch this video. Someone (a monitor mix engineer perhaps?) must have secretly recorded this audio.
I do believe it is authentic...but on the other hand, and credit to Britney...her microphone is normally "off" during her performances. The actual original recording song playback is what comes through the FOH (front of house)...not Britney's vocals. However, Britney continues to sing live (though no one USUALLY hears it). Yup, Britney is indeed singing...but just not the right notes. BWWWWHAHAHAHAHAAHAAHAHAAAHAA.
And let's not forget Britney's #1 classy moment "Hey My PUSSY is hanging out!"