Hart, 21, returns to the Fenmen from Southern League side Yaxley.
He made a total of 84 appearances for the club in previous stints, which started with a youth loan from Peterborough United in September 2017.
Manager Brett Whaley said: "In our short period in charge last season I felt 'Azza' was one of our better players, so I’m delighted to have him back on board. He’s got experience of the league and the club, and strengthens us massively.
"The squad is looking much stronger than when we went into lockdown, and we now need to prepare for whenever the restart is confirmed."
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