Spender.sol

pragma solidity 0.4.11;

contract TokenTransferProxy is Ownable {

    modifier onlyAuthorized {
        require(authorized[msg.sender]);
        _;
    }
    
    modifier onlyApprovedByUser(address user) {
        require(approvedByUser[user][msg.sender]);
        _;
    }

    mapping (address => bool) public authorized;
    
    mapping (address => mapping (address => bool) public approvedByUser;
    
    function transferFrom(address token, address from, address to, uint value)
        public
        onlyAuthorized
        onlyApprovedByUser(from)
        returns (bool)
    {
        return Token(token).transferFrom(from, to, value);
    }
    
    function approve(address spender) public {
        require(authorized[spender]);
        authorizedByUser[msg.sender][spender] = true;
    }
    
    function unapprove(address spender) public {
        authorizedByUser[msg.sender][spender] = false;
    }
}