Policy Authoring

Status: DRAFT

1. Overview

APS supports two complementary policy authoring models. They can be mixed within the same policy set.

Model	Best for
Rego	Declarative rules, composable logic, OPA ecosystem compatibility
Runtime	Rules requiring external I/O, complex state, or typed business logic

2. Rego Policies

APS Rego policies are standard OPA policies evaluated against a structured input document. Each interception point has its own package namespace:

Interception Point	Package
Input	aps.input
Tool Call	aps.tool_call
Output	aps.output

2.1 Required Rules

A compliant Rego policy MUST define a decision rule that produces one of: allow, deny, redact, transform, audit.

package aps.input

default decision := "allow"

decision := "deny" if { ... }

2.2 Optional Rules

Rule	Type	Description
reason	string	Human-readable explanation for the decision
redactions	array	Required when decision == "redact"
transformation	object	Required when decision == "transform"

2.3 Input Document

The input document corresponds to the context object for each interception point. See Core Concepts §4 for the full schema.

3. Runtime Rules

Runtime rules implement a typed interface provided by the APS runtime SDK. They are registered alongside Rego policies and evaluated in the same pipeline.

3.1 Java Interface (planned)

public interface InputPolicy {
    PolicyDecision evaluate(InputContext context);
}

public interface ToolCallPolicy {
    PolicyDecision evaluate(ToolCallContext context);
}

public interface OutputPolicy {
    PolicyDecision evaluate(OutputContext context);
}

3.2 TypeScript Interface (planned)

interface InputPolicy {
  evaluate(context: InputContext): PolicyDecision;
}

interface ToolCallPolicy {
  evaluate(context: ToolCallContext): PolicyDecision;
}

interface OutputPolicy {
  evaluate(context: OutputContext): PolicyDecision;
}

3.3 PolicyDecision Shape

type PolicyDecision =
  | { decision: "allow" }
  | { decision: "deny"; reason?: string }
  | { decision: "redact"; redactions: Redaction[] }
  | { decision: "transform"; transformation: Transformation }
  | { decision: "audit" };

4. Policy Set Configuration

A policy set is the full collection of policies applied to a single APS runtime instance. It is declared in a configuration file (format TBD — candidates: YAML, JSON).

policy_set:
  on_error: deny        # or: allow
  input:
    - type: rego
      path: policies/no-ssn.rego
    - type: runtime
      class: com.example.policies.ContentFilterPolicy   # Java
  tool_call:
    - type: rego
      path: policies/approved-tools.rego
  output:
    - type: rego
      path: policies/no-blocked-domains.rego
    - type: runtime
      class: RedactCreditCardPolicy                     # TypeScript