It's been a nice sunny day here too, but with a nasty cold wind.
An authoriser is someone who has the the authority, or permission, to sign purchase orders and in effect spend the company's money. At work I was the Team Leader and if we needed to buy any supplies for our unit I had the company's permission to place the order and spend the money, without asking my manager first, and our accounts department would pay the supplier because I had signed and "authorised" the purchase.