In decentralized applications, unlike traditional web applications that rely on centralized databases and authentication, has its own challenges and opportunities. To this end, smart contract-based authentication serves as the backbone of managing user registration and login using Ethereum addresses as unique identifiers.
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Below is the code for a basic authentication contract:
In the above code:
pragma solidity ^0.8.0; specifies the Solidity compiler version to use, ensuring compatibility
contract BasicAuth begins the declaration of a new contract called ‘BasicAuth’
struct User {string username; bool exists;} represents a user within a smart contract containing two fields:
username of the string data type that holds the username of the users
exists of the boolean data type that indicates whether a user has been registered in the contract
mapping(address => User) private users; declares a mapping named users, which is a key-value store for associating Ethereum addresses with User structs.
event UserRegistered(address userAddress, string username); emits an event containing the address and username of the user when a new user is registered in the system.
event UserLoggedIn(address userAddress); emits the ‘UserLoggedIn’ event, including the user’s address as an argument, when a user logs into the system.
function register(string calldata _username) external {
require(!users[msg.sender].exists, “User already exists”);
users[msg.sender] = User({
username: _username,
exists: true
});
emit UserRegistered(msg.sender, _username); } onboards a new user to the contract, associating a unique Ethereum address (‘msg.sender’) with a ‘username’.
require(!users[msg.sender].exists, “User already exists”); checks if a user already exists as a registered user.
users[msg.sender] = User({username: _username, exists: true}); creates a new ‘User’ struct if the user does not already exist and assigns to the caller’s address in the ‘users’ mapping.
function login() external {
require(users[msg.sender].exists, “User does not exist”);
emit UserLoggedIn(msg.sender); } declares a function named ‘login’ with ‘external’ visibility, so it can only be called from outside the contract.
‘require(users[msg.sender].exists, “User does not exist”);’ checks if the caller of the function ‘msg.sender’ is registered as a user in the contract
If the check passes indicating the user does exist, ‘emit UserLoggedIn(msg.sender);’ emits the ‘UserLoggedIn’ event with ‘msg.sender’ as its parameter.
function getUsername() external view returns (string memory) {
require(users[msg.sender].exists, “User does not exist”);
return users[msg.sender].username; } retrieves the username associated with the Ethereum address of the caller (‘msg.sender’).
‘require(users[msg.sender].exists, “User does not exist”);’ checks is the user exists in the contract.
If the check passes indicating the user does exist, return users[msg.sender].username; returns the ‘username’ associated with the caller’s address.
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