WebAC authorization Fedora module is an implementation of the still evolving draft by the W3C that proposes a decentralized authorization mechanism. See WebAccessControl specifications at the W3C website. 

W3C's definition of WebAccessControl:

WebAccessControl is a decentralized system for allowing different users and groups various forms of access to resources where users and groups are identified by HTTP URIs. 

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User -> Read/Write/Append/Control -> Resource/ResourceType

Example:

1. userA can Read document foo
@prefix acl: <http://www.w3.org/ns/auth/acl#>

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</acls/write> acl:accessToClass </objecttype/news> ;
acl:mode acl:Read, acl:Write;
acl:agentClass </agents/newsEditor> .

Steps in determining the effective authorization:

1. Get the ACL of the requested resource.
   1.  if ACL exists:
      1. Find union of authorizations that specify access for the requesting user. This includes:
         1. authorizations that specify accessTo to the requested resource.
         2. authorizations that specify accessToClass of the requested resource type.
      2. Find union of authorizations that specify access for the requesting user's group. This includes:
         1. authorizations that specify accessTo to the requested resource.
         2. authorizations that specify accessToClass of the requested resource type.
      3. If authorizations exist for user or group:
         
         1. Find the union of authorizations found from steps 1.a.i and 1.a.ii.
         2. Go to step 4.
      4. if no authorization exist for user or group:
         1. Deny Access. Go to step 2.
   2. if no ACL exists for requested resource:
      1. Go to step 2.
2. Get the ACL of the next ancestor (using either ldp:contains or fedora:hasParent).
   1.  if ACL exists:
      1. Find union of authorizations that specify access for the requesting user. This includes:
         1. authorizations that specify accessTo to the requested resource.
         2. authorizations that specify accessToClass of the requested resource type.
      2. Find union of authorizations that specify access for the requesting user's group. This includes:
         1. authorizations that specify accessTo to the requested resource.
         2. authorizations that specify accessToClass of the requested resource type.
      3. If authorizations exist for user or group:
         
         1. Find the union of authorizations found from steps 2.a.i and 2.a.ii.
         2. Go to step 4.
      4. Find union of authorizations that specify access for the requesting user. This includes:
         1. authorizations that specify accessTo to the requested resource's ancestor.
      5. Find union of authorizations that specify access for the requesting user's group. This includes:
         1. authorizations that specify accessToClass of to the requested resource's ancestor.
      6. If authorizations exist for user or group:
         
         1. Find the union of authorizations found from steps 2.a.iv and 1.a.v.
         2. Go to step 4.
      7. if no authorization exist for user or group:
         1. Deny Access. Go to step 2.
   2. if no ACL exists for the current ancestor resource:
      1. Go to step 2.
3. If no more ancestor exist (root node reached) and no ACL or no matching authorization is found:
   1. Deny access.
4. Use the most permissive from the set of authorizations found.
   1. Grant access if the authorizations permit requested access mode (read, write, append).
   2. Deny access if the authorizations does not permit requested access mode.

Example Request Authorization Flow:

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