How can I grant access to my AdWords account for third-party app?

[Łukasz Tarasiewicz]

Hello, 

A friend of mine will develop an application that will read data from my AdWords accounts.

We're not sure how I can grant read-only access for his application so that it can access my data:

1) Should I create a "new project" in my Google Developer Console account and pass on to him my clientID and clientSecret so that he can use it later to generate refreshToken?

2) Or perhaps, if he has already authorized the application to have access to HIS Manager Account, I should now link my AdWords account with his ManagerAccount for read-only access?

and finally

3) Should I authorize my developerToken with Google  and pass the token for him, or he should authorize his token and use it?

This is a simple application that will download reports for my AdWords accounts but we're not sure how I authorize his app. Personally I like option 2 above the most.

I'd appreciate your advice, thank you.