CIAM 102: Autorisierung & Rollenbasierte Zugriffskontrolle

Background#

In the previous article, we introduced the concept of authentication (AuthN) and authorization (AuthZ), along with some headachy terms: Identity, Organization, Tenant, etc.

Organization and Tenant are great for grouping Identities, but they lead to an absolute democracy: everyone can do anything in this system. While utopia is still a mystery, let’s take a look at the governance of access: Authorization (AuthZ).

Why do we need authorization?#

Notion is a great example. For each page you own, you can choose to keep it private, accessible only to you, or share it with friends, or even the public.

Or, for an online bookstore, you want everyone to be able to view all books, but customers to only view their own orders, and sellers to manage only the books in their stores.

AuthZ and AuthN are essential components of a complex business model. They often go hand-in-hand; AuthZ verifies a user's access, while AuthN authenticates identities. Both are necessary for a secure system.

The basic authorization model#

Here’s one of the most common AuthZ models: If IDENTITY performs ACTION on RESOURCE, then ACCEPT or DENY.

In the Notion example, the model is PERSON performs VIEW on PAGE.

If the page is private:

• You’ll receive ACCEPT when performing VIEW on your PAGE.
• Everyone else should receive DENY when performing VIEW on your PAGE.

Based on consensus, the industry developed various authorization technologies, such as Role-based Access Control (RBAC), Attribute-based Access Control (ABAC). Today, we will focus on the NIST RBAC model Level 1: Flat RBAC.

Role-based Access Control#

Let's extend the bookstore example. Say we have many customers, but only one seller:

• Customers can view and order books, as well as view their own orders.
• The seller can view, create, and delete books, and manage customer orders.

Define resources#

In Logto, a resource (i.e. API Resource) usually represents a set of entities or items, since it’s required to use a valid URL as the indicator. Hence we define two resources:

• Books: https://api.bookstore.io/books
• Orders: https://api.bookstore.io/orders

One of the advantages of enforcing the URL format is it can map to a real address of your API service, which improves the readability and recognizability when integrating with other components in the system.

Define permissions#

Since we introduced the concept of resource, in Logto, we also enforce that permissions must belong to a resource, in reverse, resources can have permissions.

Let’s add some permissions the the resources:

• Books: read, create, delete
• Orders: read, read:self, create:self, delete

Although there’s no requirement of the name of a permission, we have the convention as below:

While <action> is required to describe a permission, :<target> can be ignored to describe a general target, i.e. to all entities or items in the resource. For example:

• Permission read in resource Books means the action to read arbitrary books.
• Permission create:self in resource Orders means the action to create orders that belong to the current user.

Define roles#

In short, a role is a group of permissions. Let’s create two roles customer and seller and assign permissions to them as below:

You may notice the permission-role assignment is many-to-many relations.

Assign roles to users#

Just like role-permission assignment, user-role assignment is also a many-to-many relationship. Therefore, you can assign multiple roles to a single user, and a single role can be assigned to multiple users.

Connect to dots#

Here’s a complete relationship diagram for the Level 1 RBAC model in Logto:

In the RBAC model, permissions are always "positive", meaning the authorization judgement is simple: if a user has the permission, then accept; otherwise, reject.

Let's say Alice has the role seller, Bob and Carol have the role customer. We'll describe actions in natural language first, and transpile them to the standard authorization format: IDENTITY performs ACTION on RESOURCE, finally giving the conclusion.

• Alice wants to add a new book for sale:
  • User Alice performs create on resource Books (https://api.bookstore.io/books).
  • Since Alice has been assigned the permission create of Books according to their role seller, the result is ✅ ACCEPT.
• Alice wants to view all orders to see if the sale meets their expectation:
  • User Alice performs read on resource Orders (https://api.bookstore.io/orders).
  • Since Alice has been assigned the permission read of Orders according to their role seller, the result is ✅ ACCEPT.
• Bob wants to browse the book list to see if there’s any books they want to purchase.
  • User Bob performs read on resource Books (https://api.bookstore.io/books).
  • Since Bob has been assigned the permission read of Books according to their role cusomter, the result is ✅ ACCEPT.
• Bob wants to view Carol’s order.
  • Since it’s someone else’s order, the permission read:self of Orders does not work here.
  • User Bob performs read on resource Orders (https://api.bookstore.io/order).
  • Since Bob has no permission read of Orders, the result is ❌ DENY.

Other RBAC levels#

There are four levels in the NIST RBAC model:

• Flat RBAC
• Hierarchical RBAC
• Constrained RBAC
• Symmetric RBAC

See the paper for details if you are interested.

Logto now has the Level 1 implementation and will progress to higher levels based on community feedback. Don’t hesitate to let us know if a higher level fits your need!

In practice#

Beside the theory, we still have heavy technical works to complete in order to make the model work as expected:

• Client and auth server development
• Database design for RBAC
• Validation across different services
• Security and open-standard compliance
• Role, permission, resource management and assignment

Don’t panic. We've taken this into account and added out-of-the-box support to cover all of the above. Check out the 🔐 RBAC recipe to learn how to use RBAC in Logto.

Closing notes#

RBAC is a powerful access management model for most cases, but there’s no silver bullet. We still have some questions:

• Do I need high levels of RBAC?
• How does RBAC compare to other authorization models?
• How to define authorization model between different Organizations?