id: SKL-blockchain-BLOCKCHAINAUTHENTICATION name: Blockchain Authentication description: Web3 authentication uses cryptographic signatures to verify user identity without passwords. This guide covers Sign-In with Ethereum (SIWE), message signing, signature verification, and session manage version: 1.0.0 status: active owner: '@cerebra-team' last_updated: '2026-02-22' category: Backend tags:

• api
• backend
• server
• database stack:
• Python
• Node.js
• REST API
• GraphQL difficulty: Intermediate

Blockchain Authentication

Skill Profile

(Select at least one profile to enable specific modules)

• DevOps
• Backend
• Frontend
• AI-RAG
• Security Critical

Overview

Web3 authentication uses cryptographic signatures to verify user identity without passwords. This guide covers Sign-In with Ethereum (SIWE), message signing, signature verification, and session management for building passwordless authentication systems using blockchain wallets.

Why This Matters

• Security: Cryptographic signatures eliminate password vulnerabilities
• User Control: Users own and control their private keys
• Interoperability: Standard SIWE protocol for wallet compatibility
• Trustless: No central authority required

Core Concepts & Rules

1. Core Principles

• Follow established patterns and conventions
• Maintain consistency across codebase
• Document decisions and trade-offs

2. Implementation Guidelines

• Start with the simplest viable solution
• Iterate based on feedback and requirements
• Test thoroughly before deployment

Inputs / Outputs / Contracts

• Inputs:
  • User wallet address
  • Message to sign
  • Domain separator (for EIP-712)
  • Session expiration time
• Entry Conditions:
  • Web3 provider configured (MetaMask, WalletConnect, etc.)
  • SIWE message library available
  • Backend wallet connection ready
  • Frontend SIWE integration ready
• Outputs:
  • Verified user address
  • Authentication session token
  • Signature verification result
  • Generated nonce for signing
• Artifacts Required (Deliverables):
  • SIWE message service
  • Signature verification service
  • Session management service
  • Frontend wallet integration
• Acceptance Evidence:
  • Wallet connection successful
  • Signature verified on-chain
  • Session created and validated
  • Nonce generation working
• Success Criteria:
  • Signature verification 100% accurate
  • Session creation latency < 500ms
  • Nonce uniqueness 100% guaranteed
  • Support 1000+ concurrent users

Skill Composition

• Depends on: Authentication (10-authentication-authorization/), Wallet Connection (35-blockchain-web3/wallet-connection/)
• Compatible with: Smart Contracts (35-blockchain-web3/smart-contracts/), Cryptocurrency Payment (35-blockchain-web3/cryptocurrency-payment/)
• Conflicts with: None
• Related Skills: wallet-connection, smart-contracts

Quick Start / Implementation Example

1. Review requirements and constraints
2. Set up development environment
3. Implement core functionality following patterns
4. Write tests for critical paths
5. Run tests and fix issues
6. Document any deviations or decisions

# Example implementation following best practices
def example_function():
    # Your implementation here
    pass

Assumptions / Constraints / Non-goals

• Assumptions:
  • Development environment is properly configured
  • Required dependencies are available
  • Team has basic understanding of domain
• Constraints:
  • Must follow existing codebase conventions
  • Time and resource limitations
  • Compatibility requirements
• Non-goals:
  • This skill does not cover edge cases outside scope
  • Not a replacement for formal training

Compatibility & Prerequisites

• Supported Versions:
  • Python 3.8+
  • Node.js 16+
  • Modern browsers (Chrome, Firefox, Safari, Edge)
• Required AI Tools:
  • Code editor (VS Code recommended)
  • Testing framework appropriate for language
  • Version control (Git)
• Dependencies:
  • Language-specific package manager
  • Build tools
  • Testing libraries
• Environment Setup:
  • .env.example keys: API_KEY, DATABASE_URL (no values)

Test Scenario Matrix (QA Strategy)

Technical Guardrails & Security Threat Model

1. Security & Privacy (Threat Model)

• Top Threats: Injection attacks, authentication bypass, data exposure

• Data Handling: Sanitize all user inputs to prevent Injection attacks. Never log raw PII
• Secrets Management: No hardcoded API keys. Use Env Vars/Secrets Manager
• Authorization: Validate user permissions before state changes

2. Performance & Resources

• Execution Efficiency: Consider time complexity for algorithms
• Memory Management: Use streams/pagination for large data
• Resource Cleanup: Close DB connections/file handlers in finally blocks

3. Architecture & Scalability

• Design Pattern: Follow SOLID principles, use Dependency Injection
• Modularity: Decouple logic from UI/Frameworks

4. Observability & Reliability

• Logging Standards: Structured JSON, include trace IDs request_id
• Metrics: Track error_rate, latency, queue_depth
• Error Handling: Standardized error codes, no bare except
• Observability Artifacts:
  • Log Fields: timestamp, level, message, request_id
  • Metrics: request_count, error_count, response_time
  • Dashboards/Alerts: High Error Rate > 5%

Agent Directives & Error Recovery

(ข้อกำหนดสำหรับ AI Agent ในการคิดและแก้ปัญหาเมื่อเกิดข้อผิดพลาด)

• Thinking Process: Analyze root cause before fixing. Do not brute-force.
• Fallback Strategy: Stop after 3 failed test attempts. Output root cause and ask for human intervention/clarification.
• Self-Review: Check against Guardrails & Anti-patterns before finalizing.
• Output Constraints: Output ONLY the modified code block. Do not explain unless asked.

Definition of Done (DoD) Checklist

• Tests passed + coverage met
• Lint/Typecheck passed
• Logging/Metrics/Trace implemented
• Security checks passed
• Documentation/Changelog updated
• Accessibility/Performance requirements met (if frontend)

Anti-patterns / Pitfalls

• ⛔ Don't: Log PII, catch-all exception, N+1 queries
• ⚠️ Watch out for: Common symptoms and quick fixes
• 💡 Instead: Use proper error handling, pagination, and logging

Reference Links & Examples

• Internal documentation and examples
• Official documentation and best practices
• Community resources and discussions

Versioning & Changelog

• Version: 1.0.0
• Changelog:
  • 2026-02-22: Initial version with complete template structure