3 page DACA memo from Janet Napolitano.
This specific fact is amply referred to in numerous court proceedings as well as official and non-official letters that make news, and is not contentious.
The popular wisdom is that DACA was implemented via Obama EO is "close enough," no doubt he ordered Napolitano to implement the policy. Clearly, an EO is not required for the DACA program to exist.
You are one of the very few I have seen that understand this. Also, PDJT has already ordered a reversal of this policy.