Either the candidate did that directly, in each state, or the RNC filed them.
I called the GOP in Maine, and was told they have zero control of the certificattion, it comes to them from the RNC with the ten bucks filing fee, and voila, on the ballot.
Or, is your challenge that certifications don't exist, period?
The latter — there is no certification entity for presidential contenders.
I thought in 2008 it might be the FEC that has responsibility. But they didn’t/don’t. They deferred to the House that certifies state electors. But that is AFTER the election.
The issue has not been addressed. Individual states may have some requirement for a person to get their name on the ballot, but there is no national/Federal entity that certifies the eligibility of presidential candidates.
The court position seems to be — from 2008 — if the people elect him or her, he or she is qualified.