Authority letter

Dear Learned Members,

I am for the Plaintiffs advocate.  Defendant is Muncipality .  On behalf of municipal commissioner one of the employees i.e., X Y Z entered the wittness box to adduce the evidence.  This employee produce the letter written by the commissioner to the Judge.  The letter is like given below

To:

The Princ., civil Judge..

....

Sir,

X Y Z has given right to give the evidence on behalf of municipal commissioner.

.the judge said this is authority letter , but I argued that this not a authorisation letter , but she is not listening to me..  So I need citation to show that authorisation letter is mandatory to adduce the evidence before the court.

Kindly upload the judgements.  Thanks in advance.

Generally, the court insists only Power of attorney duly notarized, wherein the extent of such powers to represent the authority has to be specified..  Without providing POA, no court allows witness representing an institution.