Rihanna & Chris Brown making out at the Jay-z concert

Rihanna and Chris Brown aren't even trying to hide anymore -- 'cause they were apparently getting cozy at the Jay-Z concert tonight ... and, based on Twitter, everyone in Brooklyn saw it.

A pic taken from behind RiRi and Chris at Barclays Center is burning up the Internet -- they're seated in VIP ... he's on the left, she's on the right.

No physical contact -- in the photo, anyway -- but Chris' right arm is stretched around the back of Rihanna's chair. 

This reunion comes the night after Chris and Rihanna were spotted at the same table in an NYC nightclub. 

They were also seen leaving the same hotel on Wednesday -- and, for what it's worth, Chris' blind-as-a-bat GF Karrueche tweeted "Bye baby" ... just a couple hours before tonight's concert.

the former couple was caught making out at celeb hotspot, The Griffin, just the night before, which caused rumors to fly that the two are back together.

Earlier in the year, the Barbadian beauty’s father explained that he is willing to put the past in the past, and gives his daughter his blessing to reunite with Chris.

"Chris has matured a lot," Ronald Fenty told Britain's Grazia magazine. "I think everybody has to put the past behind them. And they seem to have done that. Being a couple is all up to her."