🎭Farcaster Integration

Overview

LendFriend integrates with Farcaster to provide users with a social identity layer on top of their CDP embedded wallet. This integration enhances the user experience by providing human-readable identities, social proof, and reputation while maintaining the security and programmability of CDP wallets.

What is Farcaster?

Farcaster is a decentralized social protocol built on Optimism, not a separate wallet or blockchain. It provides:

  • FID (Farcaster ID): A unique numerical identifier on the Optimism blockchain

  • Username (fname): A free, human-readable handle (e.g., alice.fcast.id displayed as @alice)

  • Social Profile: Bio, avatar, and social connections

  • Decentralized Social Graph: Portable social relationships across applications

Important Distinctions

Farcaster is NOT:

  • ❌ A separate wallet

  • ❌ A separate blockchain

  • ❌ A token or cryptocurrency

Farcaster IS:

  • ✅ A social identity layer

  • ✅ Metadata linked to your existing wallet address

  • ✅ A portable social profile and reputation system

Architecture

One Wallet, One Social Identity

When users sign up for LendFriend via CDP, they receive:

User Account
├── CDP Embedded Wallet (Primary)
│   ├── EVM Address (0x...)
│   ├── Session Keys (for auto-deduction)
│   └── Account Abstraction Features
│
└── Farcaster Profile (Social Layer)
    ├── FID (e.g., 12345)
    ├── Username (e.g., alice.fcast.id → @alice)
    ├── Profile (bio, avatar)
    └── Social Graph (followers, following)

How It Works

  1. Single Address: Users have ONE wallet address from CDP

  2. Linked FID: Farcaster FID is registered and linked to that CDP address

  3. Social Identity: Username and profile provide human-readable identity

  4. Financial Operations: CDP wallet handles all transactions, payments, and auto-deduction

  5. Social Features: Farcaster enables social discovery, reputation, and virality

Registration & Costs

Current State (October 2025+)

Farcaster registration is now FREE:

  • FID Registration: Free (previously $5-10)

  • Free Username: username.fcast.id at no cost

  • Gas Costs: ~$0.10 per registration (Optimism L2)

Username Options

  1. Free Username (fname)

    • Format: username.fcast.id

    • Displayed as: @username

    • Off-chain registration

    • Can be changed

    • Owned by Farcaster protocol

  2. Paid ENS (.eth)

    • Format: username.eth

    • On-chain ownership

    • Cannot be revoked

    • Annual renewal fees

    • User owns the ENS name

Recommendation: Start users with free fnames. They can optionally upgrade to .eth later.

Benefits of Automatic Farcaster Integration

For Users

  1. Human-Readable Identity

    • @alice instead of 0x742d...

    • Easier for friends to find and recognize

  2. Social Proof

    • Profile photo and bio

    • Follower count and social connections

    • Reputation history

  3. Better UX

    • No need to copy/paste addresses

    • Social discovery features

    • Familiar social media experience

  4. Portability

    • Same identity across all Farcaster apps

    • Not locked to LendFriend

    • Ownership and control

For LendFriend Platform

  1. Lower Friction

    • One-step signup process

    • No separate Farcaster registration needed

    • Immediate social identity

  2. Network Effects

    • Users discoverable across Farcaster ecosystem

    • Viral growth through social connections

    • Cross-platform user acquisition

  3. Trust & Reputation

    • Social connections inform trust scoring

    • Profile history provides context

    • Anti-Sybil through social graph

  4. Minimal Cost

    • ~$0.10 gas cost per user

    • Free FID and username

    • High ROI on user acquisition

Implementation Recommendations

Registration Flow

// When user signs up via CDP OAuth/Email/SMS
async function handleUserSignup(cdpAddress: string, email: string) {
  // 1. Create CDP embedded wallet (existing)
  const wallet = await createCDPWallet(email);

  // 2. Auto-register Farcaster account
  const farcasterAccount = await registerFarcasterAccount({
    custodyAddress: cdpAddress,
    username: generateUsername(email), // e.g., alice123
    requestSponsor: true, // Optional: sponsor gas costs
  });

  // 3. Store FID and username in database
  await db.users.update({
    address: cdpAddress,
    fid: farcasterAccount.fid,
    username: farcasterAccount.username,
  });

  // 4. Continue with normal onboarding
  return { wallet, farcasterAccount };
}

Username Generation Strategy

function generateUsername(email: string): string {
  // Extract name from email
  const localPart = email.split('@')[0];

  // Sanitize (alphanumeric + hyphens)
  const sanitized = localPart.replace(/[^a-zA-Z0-9-]/g, '');

  // Add random suffix if needed for uniqueness
  const username = `${sanitized}${Math.floor(Math.random() * 1000)}`;

  return username.toLowerCase();
}

User Customization

After initial signup, allow users to:

  1. Change Username: Switch to a preferred fname

  2. Update Profile: Add bio, avatar, links

  3. Upgrade to ENS: Purchase .eth name (optional)

  4. Connect Existing: Link existing Farcaster account instead of creating new

Technical Details

CDP + Farcaster Integration

Feature
Handled By

Wallet Address

CDP Embedded Wallet

Private Keys

CDP (MPC custody)

Transactions

CDP Wallet

Session Keys

CDP (auto-deduction)

Social Identity

Farcaster

Username

Farcaster

Profile

Farcaster

Social Graph

Farcaster

Security Considerations

  1. Custody: CDP maintains custody of private keys via MPC

  2. Farcaster Keys: Separate signer keys for Farcaster operations

  3. Permissions: Farcaster cannot move funds (no transaction signing)

  4. Recovery: CDP account recovery also maintains Farcaster link

Cost Analysis

Per-User Costs

  • FID Registration: $0 (now free)

  • Gas on Optimism: ~$0.10

  • CDP Account: Free (included in platform)

  • Total per user: ~$0.10

ROI Calculation

For a 10,000 user base:

  • Total cost: $1,000 (10K users × $0.10)

  • Benefits:

    • Social discovery across Farcaster ecosystem

    • Reduced friction in signup

    • Better trust scoring via social graph

    • Viral growth through social connections

    • User retention through portable identity

Expected ROI: High - minimal cost for significant UX and growth benefits

Migration Path

For Existing Users

Users who already have accounts before Farcaster integration:

  1. Prompt during login: "Add social identity to your account?"

  2. Optional registration: Let users opt-in to create Farcaster profile

  3. Link existing: Allow linking of existing Farcaster accounts

  4. Incentivize: Consider rewards for completing profile

For New Users

  • Automatic: Create Farcaster account during CDP signup

  • Seamless: No additional steps required

  • Transparent: Explain benefits in onboarding

Related Documentation

Conclusion

Recommendation: Implement automatic Farcaster account creation during CDP signup.

The benefits far outweigh the minimal costs (~$0.10/user), and the integration provides:

  • Better UX with human-readable identities

  • Social discovery and viral growth

  • Enhanced trust scoring through social connections

  • Portable reputation across the Farcaster ecosystem

Farcaster complements CDP's wallet infrastructure by adding a social identity layer without compromising security or introducing wallet fragmentation.

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