A reader cites the correct reference:
The term "Author of Liberty" comes from the fourth stanza of Samuel Smith’s hymn "America," which is sung to the tune of "Good Save the Queen."
Here’s the verse:
Our fathers’ God, to thee,
Author of liberty, to thee we sing;
Long may our land be bright
With freedom’s holy light;
Protect us by thy might, great God, our King.
I like the indirectness of the invocation of the deity. Less is sometimes more.
The Dish 