Capacitor 7 Hardware-Backed WebAuthn Level-3 Enclave Bridge Guardrail

Enforces strict isolation between Capacitor 7 hybrid WebViews and underlying hardware-backed authentication modules (Apple Secure Enclave and Android KeyStore StrongBox). All credential generation, assertion signatures, and biometric user verifications must be handled via native bridge calls returning opaque attestation payloads and WebAuthn-compliant signatures without ever exposing raw asymmetric keys, private seeds, or plaintext biometric claims to the WebView DOM or JavaScript runtime.

--- description: Capacitor 7 Hardware-Backed WebAuthn Level-3 Enclave Bridge Guardrail - Enforces strict isolation between Capacitor 7 hybrid WebViews and underlying hardware-backed authentication modules (Apple Secure Enclave and Android KeyStore StrongBox). All credential generation, assertion signatures, and biometric user verifications must be handled via native bridge calls returning opaque attestation payloads and WebAuthn-compliant signatures without ever exposing raw asymmetric keys, private seeds, or plaintext biometric claims to the WebView DOM or JavaScript runtime. globs: src/**/*.{ts,tsx}, ios/App/App/**/*.{swift,m}, android/app/src/main/**/*.{java,kt} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/capacitor-7-secure-enclave-webauthn-bridge-guardrail" --- # Capacitor 7 Hardware-Backed WebAuthn Level-3 Enclave Bridge Guardrail > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Exposing Raw Cryptographic Key Material or Simulated Biometric Tokens in Hybrid WebView DOM ## System Constraints You are a Principal Mobile Security Architect enforcing zero-trust hardware-backed credential storage in Capacitor 7 hybrid mobile applications. Never allow private key generation, handling, or parsing in the JavaScript/TypeScript layer. Ensure all WebAuthn/Passkey registration and assertion workflows delegate strictly to native Swift/Kotlin plugins that bind credentials to the Apple Secure Enclave (kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly / SecAccessControlCreateWithFlags) or Android Keystore StrongBox (setKeySize, setIsStrongBoxBacked). Ensure DOM interaction is restricted to handling opaque ArrayBuffer credentials, standard WebAuthn CBOR/DER structures, or passing server-issued nonces/challenges. ## Strict Guidelines - Engineers MUST ALWAYS isolate cryptographic private keys within the platform's hardware security module (Secure Enclave on iOS, StrongBox Keymaster on Android) using native Capacitor 7 plugin bridges. - Engineers MUST NOT generate, import, or decrypt private asymmetric keys within JavaScript/TypeScript runtime code or the WebView DOM. - Engineers MUST validate server-provided cryptographic challenges strictly against hardware-signed attestation statements or signature outputs before transmitting to backend relying parties. - Native plugins MUST enforce biometric user verification flags (UserVerificationRequirement.REQUIRED) at the hardware level, rejecting software-fallback bypasses in production builds. - Web code SHOULD only handle Base64URL-encoded authenticator data, DER-encoded signature payloads, and public credential IDs, treating all cryptographic operations as opaque RPCs. ## Bad vs Good Implementations ### Hardware-Backed WebAuthn Assertion Bridge vs. JavaScript In-Memory Signing #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Private key material is retrieved from unencrypted or standard software storage into the WebView DOM. This exposes the private key to DOM-based XSS, memory dump exploits, and supply-chain script tampering. It bypasses hardware-backed Secure Enclave / StrongBox biometric access controls. ```typescript import { Preferences } from '@capacitor/preferences'; import * as jose from 'jose'; // ANTI-PATTERN: Loading a stored raw private key into WebView memory // and executing signatures inside the DOM JavaScript sandbox. export async function signAuthenticationChallenge(challenge: string): Promise<string> { const { value: privateKeyJwk } = await Preferences.get({ key: 'user_signing_key' }); if (!privateKeyJwk) throw new Error('Key not found'); const rawKey = JSON.parse(privateKeyJwk); const privateKey = await jose.importJWK(rawKey, 'ES256'); const jws = await new jose.SignJWT({ sub: 'user_123', nonce: challenge }) .setProtectedHeader({ alg: 'ES256' }) .setIssuedAt() .sign(privateKey); return jws; } ``` #### Production Standard (Correct) > **Standard**: Delegates cryptographic operations to the native Capacitor plugin (`EnclavePasskey`). The hardware security module executes biometric verification and signs the payload internally. The WebView never accesses or controls the private key, ensuring compliance with Level-3 Hardware-Backed WebAuthn standards. ```typescript import { registerPlugin } from '@capacitor/core'; interface NativePasskeyPlugin { authenticateWithEnclave(options: { challenge: string; rpId: string; credentialId: string; }): Promise<{ clientDataJSON: string; authenticatorData: string; signature: string; userHandle?: string; }>; } const EnclavePasskey = registerPlugin<NativePasskeyPlugin>('EnclavePasskey'); // PRODUCTION FIX: The WebView only orchestrates native Hardware-Backed assertion. // Private key never leaves the Apple Secure Enclave / Android StrongBox. export async function signAuthenticationChallenge(challenge: string, credentialId: string): Promise<{ clientDataJSON: string; authenticatorData: string; signature: string; }> { // Hardware enclave directly prompts for FaceID/Biometrics and computes signature const result = await EnclavePasskey.authenticateWithEnclave({ challenge, rpId: 'auth.enterprise.com', credentialId }); // WebView receives only opaque assertions formatted per WebAuthn L3 spec return { clientDataJSON: result.clientDataJSON, authenticatorData: result.authenticatorData, signature: result.signature }; } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Capacitor 7 Hardware-Backed WebAuthn Level-3 Enclave Bridge Guardrail

Capacitor 7 Hardware-Backed WebAuthn Level-3 Enclave Bridge Guardrail defines an industrial-grade behavioral standard for mobile engineering. Enforces strict isolation between Capacitor 7 hybrid WebViews and underlying hardware-backed authentication modules (Apple Secure Enclave and Android KeyStore StrongBox). All credential generation, assertion signatures, and biometric user verifications must be handled via native bridge calls returning opaque attestation payloads and WebAuthn-compliant signatures without ever exposing raw asymmetric keys, private seeds, or plaintext biometric claims to the WebView DOM or JavaScript runtime. 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: Exposing Raw Cryptographic Key Material or Simulated Biometric Tokens in Hybrid WebView DOM 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 Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Exposing Raw Cryptographic Key Material or Simulated Biometric Tokens in Hybrid WebView DOM	Critical	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 Inconsistency	AI 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:

Engineers MUST ALWAYS isolate cryptographic private keys within the platform's hardware security module (Secure Enclave on iOS, StrongBox Keymaster on Android) using native Capacitor 7 plugin bridges.

Engineers MUST ALWAYS isolate cryptographic private keys within the platform's hardware security module (Secure Enclave on iOS, StrongBox Keymaster on Android) using native Capacitor 7 plugin bridges.

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.