Authorizers

Authorizers are components in information systems that evaluate whether a given subject should be allowed to perform a requested action on a resource. They operate after identity has been established through authentication and may incorporate additional factors such as time, location, or device posture. Authorizers enforce access control policies that can be expressed through models like role-based access control (RBAC), attribute-based access control (ABAC), or policy-based access control (PBAC), as well as through policy languages.

In practice, an authorizer may reside in an API gateway, a web application firewall, a cloud identity and access management service, or a microservices sidecar. The authorizer inspects the subject’s identity and attributes, the action, the resource, and contextual data, then returns a decision to permit or deny, sometimes accompanied by scope, claims, or constraints.

Policy languages and tooling used by authorizers include XACML, Rego with Open Policy Agent (OPA), cloud provider IAM policies, and tokens carrying authorization data such as OAuth 2.0 or OpenID Connect claims. Some systems employ centralized authorizers for governance, while others use distributed or per-service authorizers; decisions can be stateless or stateful.

Key considerations for authorizers include performance, policy complexity, data freshness, and auditability. Centralized authorizers can simplify management but may become bottlenecks; distributed approaches can improve scalability but require consistent policy administration and versioning.

See also: access control, identity and access management, OAuth, OpenID Connect, RBAC, ABAC, PBAC, XACML, and Open Policy Agent.