Implement ERC20 Token Balance Verification

[codeiaks]

Add functionality to verify that users hold a minimum balance of specified ERC20 tokens. This will allow for token-gated access to certain features or groups within the Discourse forum based on on-chain assets.

Purpose

• Enable admins to create token-gated communities within Discourse
• Verify token ownership
• Create a foundation for Web3-based permissions within the forum

Technical Requirements

• Add Web3.js integration for reading token contracts
• Implement ERC20 standard balanceOf method calls
• Create configurable minimum balance thresholds in site settings
• Develop verification UI component for admin dashboard
• Add server-side verification for token balance claims
• Build caching mechanism to prevent excessive blockchain calls

Implementation Details

The implementation will need to:

1. Allow admins to specify token contract addresses and minimum balances
2. Connect to user's wallet to verify token holdings (read-only)
3. Store verification results securely
4. Re-verify balances periodically
5. Assign users to groups based on verification results

Example Code Snippet

// Client-side token balance verification
window.checkTokenBalance = async function(tokenAddress, minAmount) {
  try {
    if (!window.ethereum) throw new Error("No wallet connected");
    
    const web3 = new Web3(window.ethereum);
    const accounts = await window.ethereum.request({ method: 'eth_requestAccounts' });
    const userAddress = accounts[0];
    
    // ERC20 minimum ABI for balanceOf
    const erc20MinABI = [
      {
        constant: true,
        inputs: [{ name: "_owner", type: "address" }],
        name: "balanceOf",
        outputs: [{ name: "balance", type: "uint256" }],
        type: "function",
      },
      {
        constant: true,
        inputs: [],
        name: "decimals",
        outputs: [{ name: "decimals", type: "uint8" }],
        type: "function",
      }
    ];
    
    const contract = new web3.eth.Contract(erc20MinABI, tokenAddress);
    const decimals = await contract.methods.decimals().call();
    const balance = await contract.methods.balanceOf(userAddress).call();
    
    const readableBalance = balance / (10 ** decimals);
    return { 
      hasMinimum: readableBalance >= minAmount,
      balance: readableBalance
    };
  } catch (error) {
    console.error("Error checking token balance:", error);
    return { hasMinimum: false, balance: 0 };
  }
};

Acceptance Criteria

• Admin can configure token addresses and minimum balances
• Users can connect wallet and verify token ownership
• Verification status is displayed in user preferences
• Users are automatically assigned to configured groups based on token ownership
• Verification is gasless (no transaction fees for users)
• System handles edge cases (disconnected wallets, contract errors)

Resources

• [ERC20 Token Standard](https://ethereum.org/en/developers/docs/standards/tokens/erc-20/)
• [Web3.js Documentation](https://web3js.readthedocs.io/en/v1.10.0/)