Okay, so step one to fighting the boss is unlocking him to fight against, this can be done by completing planets in the Illuminate system. Completing planets award influence based on how many stars you gain in missions and the difficulty level of the planet. Once you have 50 influence you can initiate the boss fight.
This boss can easily be beaten solo however if you have additional players they can bring extra Thunderer Barrages with them to speed up the process. All players should be using the Stratagem Priority perk.
You'll want to start by running towards the boss to initiate the battle then run back into a corner, immediately after arriving you'll want to drop an Incendiary Bomb in front of you using a short throw (Tap R2) and then follow it up by spamming the Thunder Barrage with a long throw (Hold R2). You'll want to carry 2 Incendiary Bombs on you so you can replenish the fire before it fades away. No enemy can pass the wall of fire and the boss will hang around just outside allowing you to damage it with Thunderer Barrages. Occasionally the boss will fire a laser attack which you can avoid by ducking backwards, be sure not to duck without facing backwards otherwise you'll dive into your fire wall.
Here's a quick video I recorded displaying the technique:
I die once due to my stupidity but the method worked a treat.