feat: new auth

[sigoden]

The access level path control used by dufs has two disadvantages:

1. One path cannot support multiple users
2. It is very troublesome to set multiple paths for one user

So it needs to be refactored.
The new auth is account based, it closes #207, closes #208.

Access Control

Dufs supports account based access control. You can control who can do what on which path with --auth/-a.

dufs -a [user:pass]@path[:rw][,path[:rw]...][|...]

1: Multiple rules are separated by "|"
2: User and pass are the account name and password, if omitted, it is an anonymous user
3: One rule can set multiple paths, separated by ","
4: Add :rw after the path to indicate that the path has read and write permissions, otherwise the path has readonly permissions.

dufs -A -a admin:admin@/:rw

admin has all permissions for all paths.

dufs -A -a admin:admin@/:rw -a guest:guest@/

guest has readonly permissions for all paths.

dufs -A -a admin:admin@/:rw -a @/

All paths is public, everyone can view/download it.

dufs -A -a admin:admin@/:rw -a user1:pass1@/user1:rw -a user2:pass2@/user2
dufs -A -a "admin:admin@/:rw|user1:pass1@/user1:rw|user2:pass2@/user2"

user1 has all permissions for /user1/* path.
user2 has all permissions for /user2/* path.

dufs -A -a user:pass@/dir1:rw,/dir2:rw,dir3

user has all permissions for /dir1/* and /dir2/*, has readonly permissions for /dir3/.

dufs -a admin:admin@/

Since dufs only allows viewing/downloading, admin can only view/download files.

BREAKING CHANGE: new auth