AgentRules.org
RulesStacksClientsAuditorPrunerSelf-HealRFCsBenchmarkCLICI/CDAuthorsSubmit
This specification is maintained by the AgentRules Working Group. Have enhancements or want to claim maintainership?Submit Specification →
securitycritical PriorityID: fido2-ror-cross-platform-origin-isolation-standard

FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation Guardrails

Enforces strict cryptographic origin binding and bidirectional verification for WebAuthn Related Origin Requests (ROR) across federated web origins and native mobile applications. Mandates mutual verification via canonical manifests (/.well-known/webauthn, assetlinks.json, apple-app-site-association) with zero tolerance for origin relaxation, preventing subdomain credential hijacking in federated architectures.

Prohibited Anti-Pattern: Unvalidated Cross-Subdomain WebAuthn Acceptance and Dynamic rpId Reflection

Export Ready-to-Drop Configuration

Select format below to copy code or download file directly.

---
description: FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation Guardrails - Enforces strict cryptographic origin binding and bidirectional verification for WebAuthn Related Origin Requests (ROR) across federated web origins and native mobile applications. Mandates mutual verification via canonical manifests (/.well-known/webauthn, assetlinks.json, apple-app-site-association) with zero tolerance for origin relaxation, preventing subdomain credential hijacking in federated architectures.
globs: src/**/auth/**/*.{ts,tsx}, src/**/webauthn/**/*.{ts,tsx}, src/**/api/auth/**/*.{ts,tsx}, server/src/**/auth/**/*.{ts,tsx}
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/fido2-ror-cross-platform-origin-isolation-standard"
---

# FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation Guardrails

> **Severity**: CRITICAL | **Category**: security
> **Anti-Pattern Warning**: Unvalidated Cross-Subdomain WebAuthn Acceptance and Dynamic rpId Reflection

## System Constraints
You are a Principal Security Architect enforcing FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation. Mandate strict cryptographic verification of WebAuthn clientDataJSON origins against authoritative Relying Party manifests, bidirectional verification between web origins and native application identifiers (Android SHA-256 fingerprint, Apple Team ID/App ID), and eliminate arbitrary rpId relaxation or dynamic origin reflection.

## Strict Guidelines
- Engineers MUST ALWAYS enforce bidirectional validation between the canonical Relying Party ID (rp.id) and related origins fetched securely from /.well-known/webauthn before accepting assertions.
- Engineers MUST NOT accept wildcard origin matching (*.example.com) or dynamically mirror incoming Host or Origin headers into Relying Party configuration.
- Services MUST verify clientDataJSON.origin against an immutable, hardcoded canonical root or an attested ROR manifest retrieved over validated HTTPS with pinned certificate expectations.
- Native mobile assertions MUST match the exact platform-specific identifier (Android package name + SHA-256 fingerprint; Apple App ID + Team ID) specified in the verified assetlinks.json or apple-app-site-association records.
- Components NEVER trust client-supplied origin claims without performing byte-for-byte base64url decoding and canonical URL schema comparison against the expected origins set.

## Bad vs Good Implementations
### Bidirectional ROR Validation vs Insecure Subdomain Suffix Matching

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Using endsWith() on clientData.origin permits subdomain takeover vectors and malicious cousin domains (e.g., https://attacker-example.com). It fails to enforce the FIDO2 ROR specification, which requires bidirectional proof between the canonical RP and the target origin via /.well-known/webauthn.
```typescript
import { AuthenticatorAssertionResponse } from '@simplewebauthn/types';

interface VerifyParams {
  response: AuthenticatorAssertionResponse;
  expectedRpId: string;
}

export async function verifyAssertionBad({ response, expectedRpId }: VerifyParams) {
  const clientData = JSON.parse(
    Buffer.from(response.clientDataJSON, 'base64url').toString('utf-8')
  );

  // VULNERABLE: Weak suffix check allows attacker.subdomain.example.com or evil-example.com
  const origin = clientData.origin;
  if (!origin.endsWith(expectedRpId)) {
    throw new Error('Unauthorized origin');
  }

  // VULNERABLE: Blindly accepting any origin ending with rpId without bidirectional ROR manifest
  return { success: true, verifiedOrigin: origin };
}
```

#### Production Standard (Correct)
> **Standard**: Normalizes and validates the origin against an exact set of cryptographically and administratively bound origins confirmed by the FIDO2 Related Origin Requests manifest. Disallows arbitrary subdomains and prevents protocol-downgrade attacks.
```typescript
import { AuthenticatorAssertionResponse } from '@simplewebauthn/types';
import { URL } from 'node:url';

interface VerifyParams {
  response: AuthenticatorAssertionResponse;
  canonicalRpId: string;
  verifiedRelatedOrigins: ReadonlySet<string>;
}

export async function verifyAssertionGood({
  response,
  canonicalRpId,
  verifiedRelatedOrigins,
}: VerifyParams): Promise<{ success: boolean; verifiedOrigin: string }> {
  const clientDataRaw = Buffer.from(response.clientDataJSON, 'base64url').toString('utf-8');
  const clientData = JSON.parse(clientDataRaw) as { origin?: string; type?: string };

  if (clientData.type !== 'webauthn.get') {
    throw new Error(`Invalid ceremony type: ${clientData.type}`);
  }

  if (!clientData.origin) {
    throw new Error('Origin missing from clientDataJSON');
  }

  const parsedOrigin = new URL(clientData.origin);
  const normalizedOrigin = `${parsedOrigin.protocol}//${parsedOrigin.host}`;

  // Verify protocol security
  if (parsedOrigin.protocol !== 'https:' && parsedOrigin.hostname !== 'localhost') {
    throw new Error('Insecure protocol for WebAuthn assertion');
  }

  // Primary canonical match or strict ROR allowlist membership
  const isCanonical = parsedOrigin.hostname === canonicalRpId;
  const isAttestedRelatedOrigin = verifiedRelatedOrigins.has(normalizedOrigin);

  if (!isCanonical && !isAttestedRelatedOrigin) {
    throw new Error(`Origin ${normalizedOrigin} is not an attested related origin for rpId ${canonicalRpId}`);
  }

  return { success: true, verifiedOrigin: normalizedOrigin };
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

Fetch MCP Server
Used to fetch and inspect /.well-known/webauthn and assetlinks.json manifests directly for origin validation.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

StepSecurity Harden-Runner
Network and execution integrity monitoring in CI to ensure origin validation test harnesses cannot be intercepted.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation Guardrails

FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation Guardrails defines an industrial-grade behavioral standard for security engineering. Enforces strict cryptographic origin binding and bidirectional verification for WebAuthn Related Origin Requests (ROR) across federated web origins and native mobile applications. Mandates mutual verification via canonical manifests (/.well-known/webauthn, assetlinks.json, apple-app-site-association) with zero tolerance for origin relaxation, preventing subdomain credential hijacking in federated architectures. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Unvalidated Cross-Subdomain WebAuthn Acceptance and Dynamic rpId Reflection Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftUnvalidated Cross-Subdomain WebAuthn Acceptance and Dynamic rpId ReflectionCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Engineers MUST ALWAYS enforce bidirectional validation between the canonical Relying Party ID (rp.id) and related origins fetched securely from /.well-known/webauthn before accepting assertions.

Engineers MUST ALWAYS enforce bidirectional validation between the canonical Relying Party ID (rp.id) and related origins fetched securely from /.well-known/webauthn before accepting assertions.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

Engineers MUST NOT accept wildcard origin matching (*.example.com) or dynamically mirror incoming Host or Origin headers into Relying Party configuration.

Engineers MUST NOT accept wildcard origin matching (*.example.com) or dynamically mirror incoming Host or Origin headers into Relying Party configuration.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Services MUST verify clientDataJSON.origin against an immutable, hardcoded canonical root or an attested ROR manifest retrieved over validated HTTPS with pinned certificate expectations.

Services MUST verify clientDataJSON.origin against an immutable, hardcoded canonical root or an attested ROR manifest retrieved over validated HTTPS with pinned certificate expectations.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Native mobile assertions MUST match the exact platform-specific identifier (Android package name + SHA-256 fingerprint

Native mobile assertions MUST match the exact platform-specific identifier (Android package name + SHA-256 fingerprint; Apple App ID + Team ID) specified in the verified assetlinks.json or apple-app-site-association records.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Components NEVER trust client-supplied origin claims without performing byte-for-byte base64url decoding and canonical URL schema comparison against the expected origins set.

Components NEVER trust client-supplied origin claims without performing byte-for-byte base64url decoding and canonical URL schema comparison against the expected origins set.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is FIDO2 Related Origin Requests (ROR) Cross-Platform Isolation Guardrails critical for AI coding assistants?

Enforces strict cryptographic origin binding and bidirectional verification for WebAuthn Related Origin Requests (ROR) across federated web origins and native mobile applications. Mandates mutual verification via canonical manifests (/.well-known/webauthn, assetlinks.json, apple-app-site-association) with zero tolerance for origin relaxation, preventing subdomain credential hijacking in federated architectures. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Unvalidated Cross-Subdomain WebAuthn Acceptance and Dynamic rpId Reflection) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

Open Specification · CC BY 4.0·Free for Personal, Team & Commercial In-Repo Use

Citation & Open Source Attribution Guidelines

This specification is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). You are completely free to adapt and share this rule in your workspace. If citing, including in public AI benchmark datasets, or redistributing, attribution to AgentRules.org is required.

Related SECURITY Rules

View all rules →
security
105

OpenFGA Graph Invariants: Cyclic Relation Prevention & Contextual Tuple Hardening

Enforces strict directed acyclic graph (DAG) topology validation during relationship mutation writes and mandates strict server-side schema verification for ephemeral contextual tuples in OpenFGA evaluations. Prohibits persistent storage of ephemeral request attributes and guards against recursive relation loops causing graph expansion denial-of-service.

security
81

WebAuthn Conditional UI Mediation, Nonce Atomicity, and Assertion Cryptographic Verification

Enforces zero-trust cryptographic validation for FIDO2/WebAuthn Passkey authentication with Conditional UI autofill. Requires atomic single-use challenge consumption to eliminate replay attacks, strict RP ID hash and origin binding, authenticatorData flag verification (User Presence and User Verification), and monotonic signature counter enforcement to detect authenticator cloning.

security
111

Enforce Sigstore Keyless OIDC Attestation and Admission Controller Verification

Enforces immutable supply-chain security using Sigstore Cosign keyless signing via ephemeral OIDC tokens issued by Fulcio and verified against the Rekor transparency log. Container workloads must be signed and attested at build time by digest, and admission controllers (such as Kyverno or Sigstore Policy Controller) must strictly validate the OIDC issuer and subject identity before allowing image execution.

1 Rule in Stack

FIDO2