Arch Lens Security

Security Architecture Lens

Cognitive Mode: Security Primary Question: "Where are the trust boundaries?" Focus: Trust Boundaries, Validation Layers, Path Contracts, Process Isolation

When to Use

• Need to understand security architecture
• Documenting trust boundaries and validation
• Analyzing path contracts and isolation
• User invokes /autoskillit:arch-lens-security or /autoskillit:make-arch-diag security

Critical Constraints

NEVER:

• Modify any source code files
• Expose actual secrets or credentials
• Show implementation details that could aid attacks
• Run subagents in the background (run_in_background: true is prohibited)

ALWAYS:

• Focus on TRUST BOUNDARIES
• Show validation layers in order
• Document path contracts and restrictions
• Include process isolation mechanisms
• BEFORE creating any diagram, LOAD the /autoskillit:mermaid skill using the Skill tool - this is MANDATORY
• If the Skill tool cannot be used (disable-model-invocation) or refuses this invocation, do NOT proceed with diagram creation. Abort this step and omit the diagram from output.
• After writing the diagram file, emit the absolute path as a structured output token as your final output. Resolve the relative temp/arch-lens-security/... save path to absolute by prepending the full CWD:

  diagram_path = /absolute/cwd/temp/arch-lens-security/{filename}.md
  

  This token is MANDATORY — the pipeline cannot proceed without it.

Arguments

/autoskillit:arch-lens-security [context_path]

• context_path (optional) — Absolute path to a PR context file containing new files (★-prefixed) and modified files (●-prefixed) from the PR diff. When provided, read this file before beginning analysis and focus the diagram on the architectural areas affected by these specific files. When absent, explore the full CWD.

Analysis Workflow

Step 0: Read PR context (when provided)

If a context_path positional argument is present:

1. Read the file at context_path
2. Extract: new files list (★-prefixed), modified files list (●-prefixed)
3. Focus Step 1 exploration on the modules/components these files belong to
4. Apply ★ prefix on diagram nodes representing new files/components
5. Apply ● prefix on diagram nodes representing modified files/components

If no context_path is provided, skip this step and explore the full CWD in Step 1.

Step 1: Launch Parallel Exploration Subagents

Spawn Explore subagents to investigate:

Input Validation

• Find input validation code
• Identify sanitization patterns
• Look for: validate, sanitize, clean, escape, input validation

Path Security

• Find path validation/restriction code
• Identify forbidden patterns
• Look for: path, traversal, .., forbidden, whitelist, blacklist

Process Boundaries

• Find subprocess/isolation code
• Identify timeouts and guards
• Look for: subprocess, Popen, timeout, isolation, sandbox

Authentication/Authorization

• Find auth-related code
• Identify permission checks
• Look for: auth, permission, token, API key, credential

Secret Management

• Find secret handling
• Identify env var usage
• Look for: secret, API_KEY, credential, .env, gitignore

File System Security

• Find file access controls
• Identify write zone restrictions
• Look for: write_zone, allowed_paths, snapshot, file_change

Database Isolation

• Find database access controls
• Identify per-user/per-tenant isolation
• Look for: isolation, tenant, scope, multi-tenancy

Step 2: Map Trust Boundaries

Identify boundaries where trust changes:

1. External -> Application (user input)
2. Application -> Subprocess (code execution)
3. Application -> FileSystem (file access)
4. Application -> Database (data access)
5. Application -> External API (outbound)

CRITICAL - Analyze Read/Write Direction: For EVERY trust boundary crossing:

• Inbound (reads): Data entering from less trusted to more trusted
• Outbound (writes): Data leaving from more trusted to less trusted
• Validation point: Where is data validated and in which direction?

Security implications by direction:

• Reads from untrusted: Requires input validation
• Writes to untrusted: Requires output encoding/sanitization
• Reads from trusted storage: Generally safe
• Writes to trusted storage: Requires authorization check

Step 3: Document Validation Layers

For each trust boundary:

• What is validated?
• How are violations handled?
• What's the defense-in-depth strategy?

Step 4: Create the Diagram

Use flowchart with:

Direction: TB for layered security view

Subgraphs per Trust Boundary:

• Entry (CLI/API input)
• Subprocess Boundary
• FileSystem Boundary
• Path Contract
• Write Zone Enforcement
• Database Isolation

Node Styling:

• cli class: Entry points, user input
• detector class: Validation gates, guards
• phase class: Processing after validation
• gap class: Forbidden/restricted (yellow warning)
• stateNode class: Enforcement points
• output class: Isolated resources

Show Flow Through Boundaries:

• Sequential validation layers
• What passes vs what's blocked

Step 5: Write Output

Write the diagram to: {{AUTOSKILLIT_TEMP}}/arch-lens-security/arch_diag_security_{YYYY-MM-DD_HHMMSS}.md (relative to the current working directory)

After writing the diagram file, emit a structured output line:

IMPORTANT: Emit the structured output tokens as literal plain text with no markdown formatting on the token names. Do not wrap token names in **bold**, *italic*, or any other markdown. The adjudicator performs a regex match on the exact token name — decorators cause match failure.

diagram_path = {absolute_path_to_diagram_file}

Output Template

# Security Diagram: {System Name}

**Lens:** Security (Trust Boundaries)
**Question:** Where are the trust boundaries?
**Date:** {YYYY-MM-DD}
**Scope:** {What was analyzed}

## Trust Boundaries Overview

| Boundary | Validation | Threat Mitigated |
|----------|------------|------------------|
| {boundary} | {validation} | {threat} |

## Security Diagram

```mermaid
%%{init: {'flowchart': {'nodeSpacing': 40, 'rankSpacing': 50, 'curve': 'basis'}}}%%
flowchart TB
    %% CLASS DEFINITIONS %%
    classDef cli fill:#1a237e,stroke:#7986cb,stroke-width:2px,color:#fff;
    classDef stateNode fill:#004d40,stroke:#4db6ac,stroke-width:2px,color:#fff;
    classDef handler fill:#e65100,stroke:#ffb74d,stroke-width:2px,color:#fff;
    classDef phase fill:#6a1b9a,stroke:#ba68c8,stroke-width:2px,color:#fff;
    classDef detector fill:#b71c1c,stroke:#ef5350,stroke-width:2px,color:#fff;
    classDef output fill:#00695c,stroke:#4db6ac,stroke-width:2px,color:#fff;
    classDef gap fill:#ff6f00,stroke:#ffa726,stroke-width:2px,color:#000;

    subgraph Boundary1 ["TRUST BOUNDARY 1: Entry"]
        INPUT["User Input<br/>━━━━━━━━━━<br/>Untrusted"]
        VALIDATE["Validation<br/>━━━━━━━━━━<br/>Check input"]
    end

    subgraph Boundary2 ["TRUST BOUNDARY 2: Subprocess"]
        PRECHECK["Pre-flight Check<br/>━━━━━━━━━━<br/>Limits check"]
        SUBPROCESS["Subprocess<br/>━━━━━━━━━━<br/>Isolated execution"]
        GUARD["Process Guard<br/>━━━━━━━━━━<br/>Timeout, cleanup"]
    end

    subgraph PathContract ["PATH CONTRACT"]
        FORBIDDEN["Forbidden Patterns<br/>━━━━━━━━━━<br/>credentials, .pem"]
        TRAVERSAL["Traversal Check<br/>━━━━━━━━━━<br/>No '..' allowed"]
        WHITELIST["Directory Whitelist<br/>━━━━━━━━━━<br/>Allowed paths"]
    end

    subgraph WriteZone ["WRITE ZONE ENFORCEMENT"]
        ZONE["Write Zone<br/>━━━━━━━━━━<br/>Restricted area"]
    end

    %% FLOW %%
    INPUT --> VALIDATE
    VALIDATE --> PRECHECK
    PRECHECK --> SUBPROCESS
    SUBPROCESS --> GUARD

    GUARD --> FORBIDDEN
    FORBIDDEN --> TRAVERSAL
    TRAVERSAL --> WHITELIST

    WHITELIST --> ZONE

    %% CLASS ASSIGNMENTS %%
    class INPUT cli;
    class VALIDATE,PRECHECK,GUARD detector;
    class SUBPROCESS phase;
    class FORBIDDEN,TRAVERSAL gap;
    class WHITELIST stateNode;
    class ZONE output;

Color Legend:

Security Validation Layers

Path Contract Rules

---

## Pre-Diagram Checklist

Before creating the diagram, verify:

- [ ] LOADED `/autoskillit:mermaid` skill using the Skill tool
- [ ] Using ONLY classDef styles from the mermaid skill (no invented colors)
- [ ] Diagram will include a color legend table

---

## Related Skills

- `/autoskillit:make-arch-diag` - Parent skill for lens selection
- `/autoskillit:mermaid` - MUST BE LOADED before creating diagram
- `/autoskillit:arch-lens-error-resilience` - For error handling view
- `/autoskillit:audit-arch` - For security violation detection