Prepare 4 x Universal-L-Brackets with a M5-Button-Head-Bolt-8mm through each of the two holes closest to the corner and a M5-Drop-In-Tee-Nut slightly threaded onto it.
Attach a Universal-L-Bracket to the inside of Extrusion-A at the four positions marked on Image 2.
Make sure the M5-Drop-In-Tee-Nuts are engaged with the slots on Extrusion-A.
The Universal-L-Brackets can now be secured to your table using 8 x Button-Head-Screws.