How to make a lens flare?

How would i go about making a lens flare in the game engine like this one:

One advice: If you’re not making a game where you play a robot then use an eye flare. A lens flare, as the name suggests, only appears in a video or picture taken by a camera. Sure it looks cool, but it’s just not realistic when you’re making a first-person medieval adventure game for example.
Ps: I don’t know how to make a lens flare.

There are lens flare too when you are behind a glass inside a car for example.

Is some complex but basically is done with particles in the Blender Game Engine.
Is need a ray sensor to know when the light hit the camera and hide or show the halo particle.