How to manage Access Control in Solidity Smart Contract
Tags: solidity, security, blockchain, web3
Published: 2024-02-22 18:17:55

Access control is a crucial aspect when developing smart contract, ensuring that only authorized users can perform certain actions within the contract.

In this article, we will cover two common techniques for implementing access control in Solidity smart contracts: the _onlyOwner_ modifier and _Role-Based_ access by leveraging OpenZeppelin contracts.

## What is OpenZeppelin
OpenZeppelin is an open-source framework designed to help developers build secure smart contracts. It offers a comprehensive suite of security tools and audit services to assist with the development, management, and inspection of all aspects of decentralized application (dApp) development.

## Manage access control using the onlyOwner modifier

OpenZeppelin's Ownable contract provides basic access control functionality. Using Ownable, you can easily add ownership control to your contract.

```
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/access/Ownable.sol";

contract SimpleContract is Ownable {
    constructor() Ownable(msg.sender) {}

    function doSomething() public onlyOwner {
        // Only the owner can call this function
    }

    function doSomethingElse() public {
        // Anyone can call this function
    }

    function changeOwnership(address newOwner) public onlyOwner {
        transferOwnership(newOwner);
    }
}

```

In the code snippet above, we:

- Imported the OpenZeppelin Ownable contract.
- Created the SimpleContract contract, which inherits from Ownable.
- Set the owner to the address of the person that deploys the contract `Ownable(msg.sender)`.
- Created a function `doSomething`, which can only be called by the owner of the contract.
- Created a function `doSomethingElse`, which can be called by anyone.
- Created a function `changeOwnership`, which can only be called by the owner to transfer ownership of the contract to another address. This function uses the transferOwnership function from the Ownable contract.

The Ownable contract also come with others functions that help manage the ownership of your smart contract easily. You can find more details about the `Ownable` contract in the [Ownable documentation](https://docs.openzeppelin.com/contracts/5.x/api/access#Ownable)


## Implement Role-Based Access Control (RBAC) using OpenZeppelin's AccessControl contract

OpenZeppelin's AccessControl contract is a powerful library for managing RBAC in Solidity. It provides a simple and modular interface for managing roles.

```
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/access/AccessControl.sol";

contract SimpleContract is Ownable, AccessControl {
    bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");

    /**
     * @dev Grants `DEFAULT_ADMIN_ROLE` to the account that deploys the contract.
     * Grants `MINTER_ROLE` to the account that deploys the contract.
     */
    constructor() Ownable(msg.sender) {
        _grantRole(DEFAULT_ADMIN_ROLE, msg.sender);
        _grantRole(MINTER_ROLE, msg.sender);
    }

    /**
     * @dev Grants `MINTER_ROLE` to the specified user.
     * Can only be called by the contract owner.
     */
    function grantMinterRole(address user) public onlyOwner {
        grantRole(MINTER_ROLE, user);
    }

    /**
     * @dev Revokes `MINTER_ROLE` from the specified user.
     * Can only be called by the contract owner.
     */
    function rovokeMinterRole(address user) public onlyOwner {
        revokeRole(MINTER_ROLE, user);
    }

    /**
     * @dev Example function that can only be called by users with the `MINTER_ROLE`.
     */
    function foo() public view {
        require(
            hasRole(MINTER_ROLE, msg.sender),
            "Should have MINTER_ROLE to call this function"
        );
        // Content of the function
    }
}
```

### Best Practices for Managing Role-Based Access Control

When implementing RBAC in Solidity, consider the following best practices:
- Use a consistent naming convention for roles.
- Limit the number of roles to minimize complexity.
- Use the principle of least privilege, granting only the minimum necessary permissions.

The AccessControl contract comes with functions that facilitate managing roles for Role-Based Access Control. You can find more details about these functions in the [AccessControl documentation](https://docs.openzeppelin.com/contracts/5.x/api/access#AccessControl).