I just completed this type of transaction in January. First make sure it is OK with your lender. Then escrow will need to draw up the POA for the specific property you are puchasing. Your lender will need to review and approve of the language. You then need to get this notorized. I suggest you use the escrow company for this. You should then be good to go.
Do plan on the signing taking longer because you will have to sign everything as his attorney in fact and this takes more time because it has to be legible and the same way every signature.
The form is called a Power of Attorney and will be either General or Specific, this will need to be notarized when created and before being recorded.
Best of luck, and congrats on the new home:)