There's no certification for heat per se; it's more that there's just a point where the aircraft can't take off safely from a given runway. Increased air temperature means increased takeoff distances for a given weight.
These are set by the manufacturer, and can be revisited as appropriate.
Not a certification limit, but you need valid performance data to be allowed to take off. So if the data is only provided up to 50 C / 122 F, then you can't take off legally at 128 F.
