How do you implement fine-grained authorization policies on the resource server?

1 Scope-based authorization

One way to implement fine-grained authorization policies on the resource server is to use scopes. Scopes are strings that represent the level of access or the type of operation that the client application can perform on the resource server. For example, a scope can be "read:profile" or "write:blog". The authorization server issues access tokens with scopes based on the user's consent and the client's registration. The resource server then checks the scopes in the access token and grants or denies access accordingly. Scope-based authorization is simple and widely supported, but it has some limitations. For instance, scopes are static and predefined, so they cannot express dynamic or complex policies. Also, scopes are coarse-grained and may not reflect the user's actual permissions or the resource's attributes.

2 Claim-based authorization

Another way to implement fine-grained authorization policies on the resource server is to use claims. Claims are key-value pairs that provide additional information about the user or the client application, such as the user's name, email, role, or group. The authorization server can embed claims in the access token, either as plain text or as a JSON Web Token (JWT). The resource server then extracts the claims from the access token and evaluates them against the authorization policies. Claim-based authorization is more flexible and expressive than scope-based authorization, as it can handle dynamic and complex policies based on the user's attributes or context. However, claim-based authorization also has some drawbacks. For example, claims can increase the size and complexity of the access token, which may affect performance and security. Also, claims may not be standardized or interoperable across different systems or domains.

3 Policy-based authorization

A third way to implement fine-grained authorization policies on the resource server is to use policy-based authorization. Policy-based authorization is a declarative and externalized approach that separates the authorization logic from the application code. The resource server relies on a policy engine or a policy decision point (PDP) to evaluate the authorization policies and return an access decision. The policies can be written in a domain-specific language (DSL) or a standard language, such as eXtensible Access Control Markup Language (XACML) or Attribute-Based Access Control (ABAC). The policies can also use various sources of information, such as the access token, the user's profile, the resource's metadata, or the environmental context. Policy-based authorization is the most advanced and granular way to implement fine-grained authorization policies on the resource server, as it can support any level of complexity and variability. However, policy-based authorization also requires more effort and expertise to design, implement, and maintain the policies and the policy engine.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?