See schematic in my previous post. I just realized that things get complicated because the op-amps need dual voltage supplies to withstand the positive and negative voltage across the shunt resistor. But I don't see another way of doing it without a CT, or hall-effect current sensor (which can also come as an IC).
I just realized the scheme I proposed would work only if your MCU power supply was isolated, Because it is impossible to wire it so the shunt resistor (with or without a rectifier) and DC power supply voltage to always have the same ground voltage if neither is isolated from the AC mains. At best, the ground voltage would only be the same 50% of the time. THe other 50% of the time would damage your MCU.
I don't see a simple way to do what you are asking. You need isolation in one point, either current measurement or DC power supply (hall effect sensor IC provides isolation without CT).