I have looked at pgadmin and phppgadmin. Neither shows any capability to work with permissions for users/groups on databases/database objects.
I thought it would be easy.! The screen would be a 2D matrix, objects down the left, users, groups on the top.
Someday, I guess I'm going to have to make a script to do that, in php, since I don't write C anymore.
If anyone knows of a graphical user interface to work with permissions, groups, and users in Postgres, let me know please.