Brake lever leaks. What to do?
Auriga M290s are generally pretty good and trouble-free but they do bite it sometimes. They're one of the most populous lower end hydros out there, but are mostly an OEM part so you won't necessarily see it listed in product lineups.

Pretty much the only reasonably fixable problem the lever might have is at the bleed port. If that's where the fluid is coming out, you can check that the o-ring underneath the screw is in good shape and sitting in there in the right place, and the bleed screw is tight. You could also check the bolt on the side of the lever, which normally isn't touched. 

You can also check that the hose connections are tight and the hose is undamaged. Especially if the bike hangs, oil that leaks out somewhere on the hose could make its way to the lever.

There isn't any internal/rebuild spare parts support for brakes like this. A complete new M290 brake is about $35US online, and that comes with a rotor and fresh pads, so just replacing the whole thing is the usual plan if there seem to be seal leaks or other internal parts issues.