Register accounts using EVM wallets

In this section, we'll walk you through creating a module for registering user accounts using EVM (Ethereum Virtual Machine) wallets. This functionality can be utilized to enable users to sign in with EVM-compatible wallets like MetaMask and can be extended to include various features such as payments.

Conceptual design

In this example, we will allow users to register an account by simply signing a message using MetaMask. This is done by using the open account registration strategy that is part of the ft library. The following sequence diagram illustrates the registration flow:

Implementation in Rell

Implementing the registration flow starts with creating a new module named registration. Keeping registration as a separate module makes it easy to include or remove this capability from the app and allows multiple registration methods. Follow these steps:

1. Create a folder named registration and within it, create a file called module.rell.

2. Add the following definitions to registration/module.rell:

src/registration/module.rell

module;

import ^.news_feed.*;
import lib.ft4.accounts.strategies.open;
import lib.ft4.accounts.strategies.{ register_account };

operation register_user(name) {
    val account = register_account();
    val user = create user ( name, account.id, account );
    create follower ( user = user, follower = user );
}

• The open strategy allows users to register themselves.
• The register_user operation first registers an account, then creates the relevant entities holding the user name and follower information.
• The register_account function ensures the transaction is signed by a unique EVM account.

3. Add an exclusion for this operation in your chromia.yml file, which tells the ft library that the register_user operation is safe to use:

chromia.yml

blockchains:
  news-feed:
    module: main
    moduleArgs:
      lib.ft4.core.auth:
        evm_signatures_authorized_operations:
          - register_user

For more details on configuring your chromia.yml file, you can refer to the Chromia Project Configuration documentation.

4. In your main.rell file, add an import statement for the new registration module:

src/main.rell

module;

import news_feed.*;
import registration.*;

caution

Even though the register_user operation requires a valid EVM signature, it exposes a potential DDOS attack vector since each account is represented as a row in the database. Mitigation strategies include:

• Rate limiting the operation.
• Enforcing payments.
• Setting up an authentication server as a middle layer.