It is not clear why u need authority letter to make anyone authorized to sign the documents related to ESI & PF or u authorized someone to represent on behalf of your company to appear in the court.
I am attaching herewith a simple authority letter which can be used for both purposes. If this letter can't solve ur purpose then right me the exact reason for which u want an authority letter
27th September 2007 From China, Beijing
18th August 2014 From India, Ghaziabad