The goalkeeper got his first real taste of first-team action during 2012-13, making 11 appearances.
Bentley made his professional debut as a substitute in the 4-1 win against Torquay United in October 2011.
His next appearance also came as a substitute as he came on for the injured Paul Smith in a 1-0 defeat at Gillingham.
Bentley made a name for himself in the FA Cup when he saved two penalties as Blues beat League 1 Bury.
He was again the penalty hero in the JPT as he saved Alfie Potter’s spotkick to ensure Blues progressed to the Area Final at the expense of Oxford.
He kept the first clean sheet of his career against Bristol Rovers in April 2013 and made it two in a row as Blues beat Aldershot Town 2-0 three days later.
Bentley played in all but one game during the 2013-14 season, keeping 20 clean sheets in all competitions.
The goalkeeper will wear the number one jersey for the first time during 2014-15.