While shifting authority from one person to another usually a Letter of Authorization is written. It is a formal letter which tells the transfer of authority along with the terms and conditions. You are provided with a sample here, you just have to write your name and the name of the person to whom you are transferring the authority along with his complete address and contact information. You also have to write the terms and conditions of the transfer of authority so that any sort of misunderstandings should be removed.
Download Letter of Authorization Doc: Download link
Download Letter of Authorization PDFs: Download link