Is it compulsory to obtain an authorization letter to drive someone?
Legally it's not required. But it's desirable to possess a letter obtained from the registered owner of the vehicle. By this letter it implies that the registered owner is aware of his liability in the event of the vehicle getting involved in any situation - like accident, theft etc. The traffic enforcement personnel (as also the personnel posted at Reserve Forest Check Post) would verify the documents of the vehicle - in that event it needs to be proved that the vehicle is being used by a bonafide person.