In WebAC you can use the acl:agentGroup property of an Authorization to point to a resource that holds a list of usernames. This allows you to create and manage groups of users within Fedora, and to assign different permissions to different groups. This how-to will guide you through the process of creating a resource, creating an agentGroup, and limiting access to that resource through an ACL that references that agentGroup.

Prerequisites

• a running Fedora repository
• curl

The commands in this guide assume that your Fedora repository is running at http://localhost:8080/fcrepo.

Steps

1. Create these three files:

   foo.ttl

   @prefix dc: <http://purl.org/dc/elements/1.1/>.
   
   <> dc:title "Hello, World!".

   group.ttl

   @prefix vcard: <http://www.w3.org/2006/vcard/ns#> .
   
   <> a vcard:Group;
       vcard:hasMember "testuser".

   acl.ttl

   @prefix acl: <http://www.w3.org/ns/auth/acl#>.
   
   <#groupRead> a acl:Authorization;
       acl:accessTo </fcrepo/rest/foo>;
       acl:agentGroup </fcrepo/rest/group>;
       acl:mode acl:Read.

2. Upload these resources into Fedora:

   curl -X PUT http://localhost:8080/fcrepo/rest/foo -u fedoraAdmin:secret3 \
       -H "Content-Type: text/turtle" --data-binary @foo.ttl
   curl -X PUT http://localhost:8080/fcrepo/rest/group -u fedoraAdmin:secret3 \
       -H "Content-Type: text/turtle" --data-binary @group.ttl
   curl -X PUT http://localhost:8080/fcrepo/rest/foo/fcr:acl -u fedoraAdmin:secret3 \
       -H "Content-Type: text/turtle" --data-binary @acl.ttl
   

3. Test that testuser can read the foo resource, while adminuser cannot: 

   curl -i http://localhost:8080/fcrepo/rest/foo -u testuser:password1
   curl -i http://localhost:8080/fcrepo/rest/foo -u adminuser:password2

   The first request should respond with 200 OK, while the second should be 403 Forbidden.

   To allow adminuser to also read the foo resource, we can add adminuser to the members of the group.

1. Create group.sparql with the following contents:

   group.sparql

   PREFIX vcard: <http://www.w3.org/2006/vcard/ns#>
   
   INSERT DATA { <> vcard:hasMember "adminuser" . }
   

2. Run this command to update the group and add adminuser to it:

   curl -i -X PATCH http://localhost:8080/fcrepo/rest/group \
       -u fedoraAdmin:secret3 \
       -H "Content-Type: application/sparql-update" \
       --data-binary @group.sparql

   You should receive a 204 No Content response on success.

1. Now you should be able to repeat the command from step 3 and successfully retrieve the foo resource as adminuser: 

   curl -i http://localhost:8080/fcrepo/rest/foo -u adminuser:password2

   This time, you should get a 200 OK response.

Caveats for agentGroup Groups

• For it to be useful, the names listed in the vcard:member properties of an authorization need to be names that your authentication system will provide to Fedora. Remember, Fedora does no authentication of its own.
• The purpose of the acl:agentGroup groups is distinct from any group mechanism your existing authentication system may have (e.g., LDAP or ActiveDirectory groups). The groups provided by the authentication system would be passed to Fedora as security principals, which the WebAC module compares against the acl:agent property. In other words, externally defined groups are opaque to Fedora, thus it treats them as simple agents.

Differences from 4.x

The WebAC implementation in Fedora 4.x used the acl:agentClass predicate to point to group listing resources, and those group listing resources were expected to have the class foaf:Group and identify their members using the foaf:member property. We have changed this implementation in Fedora 5.x to align with the "Groups of Agents" section of the SOLID WebAC specification.