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RBAC

Role definition

[role_definition] is the definition for the RBAC role inheritance relations. Casbin supports multiple instances of RBAC systems, e.g., users can have roles and their inheritance relations, and resources can have roles and their inheritance relations too. These two RBAC systems won't interfere.

This section is optional. If you don't use RBAC roles in the model, then omit this section.

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

The above role definition shows that g is a RBAC system, and g2 is another RBAC system. _, _ means there are two parties inside an inheritance relation. As a common case, you usually use g alone if you only need roles on users. and you can use g and g2 when you need roles (or groups) on both users and resources. Please see the rbac_model.conf and rbac_model_with_resource_roles.conf for examples.

Casbin stores the actual user-role mapping (or resource-role mapping if you are using roles on resources) in the policy, for example:

p, data2_admin, data2, read
g, alice, data2_admin

It means alice inherits/is a member of role data2_admin. alice here can be a user, a resource or a role. Casbin only recognizes it as a string.

Then in a matcher, you should check the role as below:

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

It means sub in the request should has the role sub in the policy.

There are several things to note:

1. Casbin only stores the user-role mapping.
2. Casbin doesn't verify whether a user is a valid user, or role is a valid role. That should be taken care of by authentication.
3. Do not use the same name for a user and a role inside a RBAC system, because Casbin recognizes users and roles as strings, and there's no way for Casbin to know whether you are specifying user alice or role alice. You can simply solve it by using role_alice.
4. If A has role B, B has role C, then A has role C. This transitivity is infinite for now.

Role hierarchy

Casbin's RBAC supports RBAC1's role hierarchy feature, meaning if alice has role1, role1 has role2, then alice will also have role2 and inherit its permissions.

Here is a concept called hierarchy level. So the hierarchy level for this example is 2. For the built-in role manager in Casbin, you can specify the max hierarchy level. The default value is 10. It means an end user like alice can only inherit 10 levels of roles.

// NewRoleManager is the constructor for creating an instance of the
// default RoleManager implementation.
func NewRoleManager(maxHierarchyLevel int) rbac.RoleManager {
    rm := RoleManager{}
    rm.allRoles = &sync.Map{}
    rm.maxHierarchyLevel = maxHierarchyLevel
    rm.hasPattern = false

    return &rm
}

How to distinguish role from user?

Casbin doesn't distinguish role from user in its RBAC. They are all treated as strings. If you only use single-level RBAC (a role will never be a member of another role). You can use e.GetAllSubjects() to get all users and e.GetAllRoles() to get all roles. They just list all u and all r respectively in all g, u, r rules.

But if you are using multi-level RBAC (with role hierarchy), and you application doesn't record whether a name (string) is a user or a role, or you have user and role with same name. You can add a prefix to role like role::admin before passing it to Casbin. So you will know if it's a role by checking this prefix.

How to query implicit roles or permissions?

When a user inherits a role or permission via RBAC hierarchy instead of directly assigning them in a policy rule, we call such type of assignment as implicit. To query such implicit relations, you need to use these 2 APIs: GetImplicitRolesForUser() and GetImplicitPermissionsForUser instead of GetRolesForUser() and GetPermissionsForUser. For more details, please see this GitHub issue.

Use pattern matching in RBAC

Sometimes, you want some subjects (or objects) with the specific pattern to be automatically granted to a role. Pattern matching functions in RBAC can help you do that. A pattern matching function shares the same parameters and return value as the previous matcher function.

We know that normally RBAC is expressed as g(r.sub, p.sub) in matcher. Then we will use policy like:

p, alice, book_group, read
g, /book/1, book_group
g, /book/2, book_group

So alice can read all books including book 1 and book 2. But there can be thousands of books and it's very tedious to add each book to the book role (or group) with one g policy rule.

But with pattern matching functions, you can write the policy with only one line:

g, /book/:id, book_group

Casbin will automatically match /book/1 and /book/2 into pattern /book/:id for you. You only need to register the function with the enforcer like:

e.rm.(*defaultrolemanager.RoleManager).AddMatchingFunc("KeyMatch2", util.KeyMatch2)

You can see the full example here.

it's notable that:

1. Only the 1st arg (aka the user) in g supports pattern functions. You are using it in 3rd arg (domain), which is currently not supported.

Role manager

The role manager is used to manage the RBAC role hierarchy (user-role mapping) in Casbin. A role manager can retrieve the role data from Casbin policy rules or external sources such as LDAP, Okta, Auth0, Azure AD, etc. We support different implementations of a role manager. To keep light-weight, we don't put role manager code in the main library (except the default role manager). A complete list of Casbin role managers is provided as below. Any 3rd-party contribution on a new role manager is welcomed, please inform us and I will put it in this list:)

Role manager	Author	Description
Default Role Manager (built-in)	Casbin	Supports role hierarchy stored in Casbin policy
Session Role Manager	EDOMO Systems	Supports role hierarchy stored in Casbin policy, with time-range-based sessions
Okta Role Manager	Casbin	Supports role hierarchy stored in Okta
Auth0 Role Manager	Casbin	Supports role hierarchy stored in Auth0's Authorization Extension

For developers: all role managers must implement the RoleManager interface. Session Role Manager can be used as a reference implementation.