Extend access context to support notion of delegation

Proposal - Provide delegated access control • Add a new property acc:type=acc:delegated to identify that the accessContext should be read from another resource, using the acc:accessContext value. Clients SHOULD detect infinite delegation loops. To reduce the cost of client processing, servers SHOULD NOT use more than 5 levels of delegation for a given access context. Example: Some work items are assigned to iteration 30, which is being managed by team A. I want an easy way to be able to change that team assignment from team A to team B, so I do not want to embed the team access context in every work item. < https://a.example.com/defect/2314 > acc:accessContext < https://a.example.com/access/context12345 > . < https://a.example.com/defect/5678 > acc:accessContext < https://a.example.com/access/context12345 > . < https://a.example.com/access/context12345 > a acc:AccessContext ; dcterms:title "Iteration 30 access context" ; dcterms:description "This is the access context for work items for iteration 30; it delegates to the access context for the team currently responsible for that iteration." ; acc:type acc:delegated ; acc:accessContext < https://a.example.com/access/context56789 > . < https://a.example.com/access/context56789 > a acc:AccessContext ; dcterms:title "Team B access context" ; dcterms:description "This is the access context for the team for team B; various iterations delegate to me." .