Green’s Dictionary of Slang

to curry favour.

1963		Dundes & Schonhorn ‘Kansas University Sl.: A New Generation’ in AS XXXVIII:3 169: To curry favor with a professor: brownie.
1989		H. Rawson Dict. of Invective (1991) 61: The sycophant may also be said to brown [someone], to get nose with [someone], to be a brownie (also with allusion to a junior Girl Scout), or to receive brownie points.