用passport-jwt验证token时报错'JwtStrategy requires a function to retrieve jwt from requests '

Question

用passport-jwt验证token时报错'JwtStrategy requires a function to retrieve jwt from requests (see option jwtFromRequest)'
代码如下

const JwtStrategy = require('passport-jwt').Strategy,
ExtractJwt = require('passport-jwt').ExtractJwt;
const mongoose = require("mongoose");
const User = mongoose.model("users");
const keys = require("../config/keys");

const opts = {}
opts.JwtFromRequest = ExtractJwt.fromAuthHeaderAsBearerToken();
opts.secretOrKey = keys.secretOrKey;

module.exports = passport => {
  passport.use(new JwtStrategy(opts , (jwt_payload , done) => {
    console.log(jwt_payload);
    User.findById(jwt_payload.id)
        .then(user => {
            if(user){
                return done(null,user);
            }
            return done(null,false);
        })
        .catch(err => console.log(err));
  }));
}

报错
throw new TypeError('JwtStrategy requires a function to retrieve jwt from requests (see option jwtFromRequest)');

Answer 1

var opts = {
  jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
  secretOrKey: keys.secretOrKey,
};

改成这样没有报错了，但是为什么？