Mob-connected Nassau County detective Hector Rosario tried to sick authorities on a rival family’s illicit gambling den — and even told local prosecutors the coffee-connected password to get inside, witnesses testified Thursday.

The cop — allegedly on the take from the Bonanno crime family to the tune of $1,500 per month — walked into the Nassau County District Attorney’s Office and told them the secret saying to get into the backroom casino at the Gran Caffe Gelateria in Lynbrook, DA Det. John Clinton said from the stand in Brooklyn federal court.

“You go by the counters, ask for an espresso or cappuccino [and] say you knew someone named Kelly — and you would be able to go to the back,” Clinton told the jury as he recounted his conversation with Rosario.

Rosario also told authorities about the building’s security cameras — but that aroused prosecutors’ suspicions, since he wouldn’t tell them exactly how he knew.

The ex-cop said something about an informant who tipped him off — but demurred when Clinton asked the meet the source and said it wasn’t possible, the detective testified.

Rosario, 51, has been charged with obstructing a grand jury probe into racketeering and lying to the FBI as he conspired target rival Genovese and Gambino Mafiosos during a feud that erupted after a profit-sharing scheme between the families went south.

On the trial’s opening day, prosecutors introduced the jurors to a laundry list of alleged mobsters and mapped out a constellation of illegal gambling operations — which led to a sweeping 2022 bust that rounded up eight alleged mobsters and Rosario.