Smart contract for logging into a front-end with public address

login.sol

pragma solidity ^0.4.18;

contract login {
    address creator;
    
    struct account {
        bytes32 username;
        bool admin;
    }
    
    mapping(address => account) accounts;
    
    function login() public {
        creator = msg.sender;
        accounts[creator].admin = true;
    }
    
    function addUser (bytes32 _username) public {
        accounts[msg.sender].username = _username;
        accounts[msg.sender].admin = false;
    }
    
    function signIn () public {
        require(msg.sender)
    }
}