This is a general letter of authorization, and you can use this letter format and wording for many types of authorization letters. For more specific and tailored authorization letters, see the other samples on this site.
[Your letterhead, if desired; if not, your return address]
[Date of letter-month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
I hereby authorize you to perform plumbing repairs in my home at 1239 Plumb Avenue, as previously discussed. The repair date that we agreed upon is August 17. I look forward to seeing you then, and please let me know if you have questions in the meantime.