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Prema Ananda
Prema Ananda Subscriber

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Building a Pay-Per-Use AI Agent Marketplace with Auth0 + Web3

#devchallenge #ai #authentication #auth0challenge

Auth0 for AI Agents Challenge Submission

This is a submission for the Auth0 for AI Agents Challenge

What I Built

AgentBounty is a marketplace where AI agents authenticate via Auth0, execute tasks, and users pay per-use in USDC with gasless transactions.

Key Innovation: Auth0 (authentication) + X402 Protocol (payment gating) + EIP-712 (gasless signatures) = Perfect AI monetization stack.

The Problem

Building AI agent marketplaces requires solving multiple authentication and security challenges:

Challenge Traditional Approach Auth0 Approach
🔐 User Authentication Build OAuth2 flows from scratch Ready in minutes
🌐 Social Login Integrate each provider separately Toggle switches in dashboard
🔒 MFA/2FA Custom implementation Built-in feature
📊 User Metadata Design database schema + API Management API included
⚖️ GDPR Compliance Legal review + implementation Handled automatically
🛡️ Security Updates Manual patching and monitoring Automatic updates

Bottom Line: Auth0 let me skip building authentication infrastructure and focus on what makes my product unique: AI agent integration, Web3 payments, and user experience.

Tech Stack

  • Auth: Auth0 OAuth2 + Management API + Async Payment Approval
  • Backend: FastAPI (Python), SQLite
  • Frontend: Vanilla JS, Tailwind CSS
  • AI: Google Gemini API, Bright Data MCP Server
  • Payments: X402 Protocol, EIP-712, ERC-3009
  • Blockchain: Base Sepolia, USDC

🎬 Demo

🔗 Links

🎭 Quick Demo (No Registration):

🚀 Full Experience (Free Registration):

📸 Screenshots

Auth0 Universal Login (works out of the box):
Login

AI Agent Marketplace:
Homepage

FactCheck Agent Results:
FactCheck

FactCheck Agent

Gasless Payment via MetaMask:
MetaMask

Want to dive deeper? Check out these guides:

Source Code:

How I Used Auth0 for AI Agents

Auth0 isn't just "login"—it's the entire security and identity infrastructure. Here's how I used Auth0 to solve real problems:

Problem 1: User Authentication

Without Auth0, I would need to build:

# What a custom auth system requires:
- User registration endpoint
- Password hashing (bcrypt/argon2)
- Email verification system
- Password reset flow
- Session management
- CSRF protection
- Rate limiting
- Security headers
- Continuous security monitoring
...and many more security considerations
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With Auth0:

# app/main.py - Complete auth setup
from authlib.integrations.starlette_client import OAuth

# OAuth client configuration
oauth = OAuth()
oauth.register(
    name='auth0',
    client_id=settings.AUTH0_CLIENT_ID,
    client_secret=settings.AUTH0_CLIENT_SECRET,
    server_metadata_url=f'https://{settings.AUTH0_DOMAIN}/.well-known/openid-configuration',
    client_kwargs={
        'scope': 'openid profile email offline_access'
    }
)
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What I got included:

  • ✅ OAuth2 + OIDC compliance
  • ✅ PKCE for mobile security
  • ✅ Automatic token refresh
  • ✅ Secure session management
  • ✅ Brute-force protection
  • ✅ Breached password detection

Developer Benefit: I could focus on building product features instead of security infrastructure.

Problem 2: Social Login (GitHub, Google)

Traditional approach requires:

For each provider:
1. Register OAuth app on GitHub/Google/etc
2. Handle OAuth callback flow
3. Store OAuth tokens securely
4. Handle token refresh
5. Map provider user to local user
6. Handle edge cases (email changes, account linking)
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With Auth0:

Auth0 handles:

  • ✅ OAuth app credentials management
  • ✅ Token storage and refresh
  • ✅ User profile normalization
  • ✅ Account linking (same email → same user)

Configuration in Auth0 Dashboard:

  1. Go to Authentication → Social
  2. Click "Google" → Enable
  3. Click "GitHub" → Enable
  4. Done!

Developer Benefit: Adding new social providers takes minutes instead of days of integration work.

Problem 3: Web3 Wallet Linking

Challenge: Users need to link their MetaMask wallet to their Auth0 account for crypto payments.

Traditional Approach:

Where to store wallet addresses?
- Design database schema
- Create API endpoints for CRUD
- Handle updates and validation
- Ensure persistence across sessions
- Maintain separate user data store
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Auth0 Solution: User Metadata

Auth0 provides a flexible user_metadata field for storing custom user data:

# app/routers/wallet.py
@router.post("/connect")
async def connect_wallet(
    request: Request,
    data: ConnectWalletRequest,
    user: dict = Depends(require_auth)
):
    """
    Connect Web3 wallet to Auth0 account

    User must be logged in with Auth0 first.
    Verifies wallet ownership via signature.
    Saves wallet_address to Auth0 user_metadata.
    """

    auth0_user_id = user.get('sub')
    user_email = user.get('email', 'unknown')

    # Verify signature (proof of wallet ownership)
    w3 = Web3()
    message = encode_defunct(text=data.message)
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Why this works:

  1. No extra database: Wallet address stored with Auth0 user
  2. Single source of truth: One user profile, multiple attributes
  3. Persistence: Survives across sessions, devices
  4. Security: Management API requires authentication
  5. Flexibility: Can add more attributes anytime

Developer Benefit: No need to maintain separate user data storage. Auth0 becomes both authentication AND user database.

Problem 4: Async Payment Approval (2FA for Payments)

Challenge: High-value crypto payments need user confirmation before processing.

Requirements:

  • User initiates payment in browser
  • Backend holds transaction
  • User approves via separate channel (email/SMS)
  • Backend executes approved transaction
  • Must be secure and auditable

What Auth0 handles:

  • ✅ Approval email/SMS delivery
  • ✅ Secure approval links with expiration
  • ✅ Callback to your backend
  • ✅ Audit trail of all approvals
  • ✅ Replay attack prevention

Security benefits:

  1. Two-factor confirmation: User approves in separate channel
  2. Time-limited: Approval expires after 5 minutes
  3. Non-repudiation: Auth0 logs who approved what
  4. Audit trail: Every payment tied to Auth0 user_id

Lessons Learned and Takeaways

✅ What Worked Brilliantly

1. Zero Upfront Investment

Auth0 Free Tier allowed me to:
- Build entire MVP
- Launch to early users
- Validate product idea
- All at no cost

Traditional approach:
- Significant development time upfront
- Long runway before first user
- Higher risk if product doesn't work out
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2. Focus on Differentiation

With Auth0:
- Minimal time on authentication
- Maximum time on unique features (X402, AI agents, Web3)

Without Auth0:
- Significant time on authentication infrastructure
- Less time for product innovation
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3. Enterprise Features from Day 1

Features I got immediately:
✅ Brute-force protection
✅ Breached password detection
✅ MFA/2FA
✅ GDPR compliance
✅ High availability

Building these manually would take considerable effort
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4. Scalability Without Refactoring

Auth0 scales automatically:
- Small user base: Works perfectly
- Growing user base: Works perfectly
- Large user base: Still works perfectly

Custom auth system:
- Often needs refactoring as you scale
- Performance optimization required
- Infrastructure management overhead
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5. Management API = Hidden Gem

# User metadata as a database
# This eliminated the need for:
- User settings system
- Preferences storage
- Wallet linking tables
- Custom attributes database

Just use Auth0:
await auth0_service.update_user_metadata(user_id, {
    'wallet_address': '0x...',
    'preferred_chain': 'base',
    'notifications': {'email': True},
    'mcp_usage_count': 42
})
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Developer Insight: Auth0's Management API serves as user metadata storage. I built a complete user profile system without writing database migrations or CRUD APIs.

⚠️ Challenges & How I Solved Them

Rate Limits on Management API

# Problem: Hitting 429 Too Many Requests
# Solution: Aggressive caching

class Auth0Service:
    def __init__(self):
        self._token_cache = {}  # 23h TTL
        self._profile_cache = {}  # 5min TTL

    async def get_user_profile(self, user_id: str) -> dict:
        # Check cache first
        if user_id in self._profile_cache:
            profile, expires = self._profile_cache[user_id]
            if datetime.utcnow() < expires:
                return profile

        # Fetch from Auth0
        profile = await self._fetch_profile(user_id)

        # Cache for 5 minutes
        self._profile_cache[user_id] = (
            profile,
            datetime.utcnow() + timedelta(minutes=5)
        )

        return profile

# Result: Drastically reduced API calls
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For AI Agent Platforms (like AgentBounty)

Advantages:

  • ✅ User metadata perfect for agent preferences
  • ✅ M2M authentication for automated systems
  • ✅ Async Payment Approval for safe transactions
  • ✅ Audit trail for compliance
  • ✅ Scales with usage

Considerations:

  • ⚠️ Need custom logic for wallet linking (straightforward to implement)
  • ⚠️ Management API rate limits (solved with caching)

Verdict: Well-suited for this use case.

🔗 Try It Yourself

🙏 Closing Thoughts

Building AgentBounty taught me that identity is infrastructure—just like databases, message queues, and cloud storage.

You don't build PostgreSQL from scratch. You don't build Kafka from scratch. You shouldn't build authentication from scratch.

Auth0 let me focus on what makes AgentBounty unique: X402 payments, AI agents, Web3 integration. The authentication layer was handled efficiently.

To other developers: If you're building anything that needs users, consider using Auth0. It's a practical choice that lets you focus on your product's unique value.

Built with Auth0 for the Auth0 for AI Agents Challenge

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