区块链技术集训营w2_2的作业

1. 通过approve将teacher设置为用户b
2. 用户b通过Teacher合约调用update方法，但是在onlyTeacher里面，msg.sender是Teacher的合约地址，想要让msg.sender == 用户b的条件没办法成立
3. 请问update里面可以拿到用户b的地址吗，要怎么做权限控制

//  SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Score {

  mapping(address => uint) public scores;
  address public teacher;
  address public owner;

  constructor() {
    owner = msg.sender;
  }

  function update(address _student, uint _score) external onlyTeacher {
    scores[_student] = _score;
  }

  function approve(address _teacher) external onlyOwner {
    teacher = _teacher;
  }

  modifier onlyOwner() {
    require(msg.sender == owner, "only owner");
    _;
  }

  modifier onlyTeacher() {
    // msg.sender是Teacher合约地址，teacher是授权的用户地址
    require(msg.sender == teacher, "only teacher can update score");
    _;
  }
}

interface IScore {
  function update(address, uint) external;
}

contract Teacher {
  function updateScore(address _addr, address _student, uint _score) public {
    IScore(_addr).update(_student, _score);
  }
}