create user
IST ? /user ? name="username" & password = "pasword"
SOLL PUT /users/otto&password="password"

create or update group 
IST PUT groups ? name = "meinegruppe" & members = [a, b, c] 
SOLL PUT /groups/name &members=a,b,c => CREATED

delete user
IST DELETE /user ? name="username"
DELETE /users/otto

delete group
IST DELETE /group ? name = "name"
DELETE /groups/48

add user to group
IST not supported
SOLL PUT /groups/48/users/otto

remove user from group
IST not supported
SOLL DELETE /groups/48/users/otto
