ReBAC

What is ReBAC?​

ReBAC (Relationship-Based Access Control) bases authorization on relationships between entities (user–resource, resource–type, etc.), not only on roles or attributes. It fits systems with rich relationship graphs: social networks, collaboration tools, multi-tenant apps.

Typical questions ReBAC answers:

• Is the user the owner of the resource?
• Is the user a member of the project that owns the resource?
• Does the resource belong to a type the user has access to?

Relationships are often modeled as graphs or paths.

ReBAC in Casbin​

Casbin models ReBAC with:

• User–resource–role relationships: “user U has role R on resource O” (e.g. alice is collaborator on doc1).
• Resource–type relationships: “resource O is of type T” (e.g. doc1 is of type doc).

Permissions are then “role R can do action A on type T”; a user gets permission if they have R on a resource that is of type T. Example model:

[request_definition]
r = sub, obj, act

[policy_definition]
p = role, obj_type, act

[role_definition]
g = _, _, _
g2 = _, _

[policy_effect]
e = some(where (p.eft == allow))

[matchers]
m = g(r.sub, r.obj, p.role) && g2(r.obj, p.obj_type) && r.act == p.act

# Permission definition: The "collaborator" role can read files of type "doc"
p, collaborator, doc, read

# User-Resource-Role Relationship: alice is a collaborator of doc1
g, alice, doc1, collaborator

# Resource-Type Relationship: doc1 is of type "doc"
g2, doc1, doc

So: the user must have the right role on the resource and the resource must match the type in the permission rule. Casbin combines g (user–resource–role), g2 (resource–type), and p (role–type–action) to decide access.