NodeJS, Passport: how to change user's password by admin - node.js

Question

I start to make admin panel for modify users. I want to have ability to change users passwords by admin. For authentication I use passport. The I change user's password - the data is saving to mongo, but after that, user can't logIn to site.
Please, help.
My Passport configuration:
module.exports = function(passport) {
passport.serializeUser(function(user, done) {
done(null, user.id)
});
passport.deserializeUser(function(id, done) {
User.findById(id, function(err, user) {
done(err, user);
});
});
passport.use('local-login', new LocalStrategy({
usernameField : 'email',
passwordField : 'password_first',
passReqToCallback : true
},
function(req, email, password, done) {
User.findOne({ 'email' : email }, function(err, user) {
if (err)
return done(err);
if (!user)
return done(null, false, function(req, res){
res.send({error: true})
});
if (!user.isAuthenticated )
return done(null, false, function(req, res){
res.send({error: true})
});
if (!user.validPassword(password))
return done(null, false, function(req, res){
res.send({error: true})
});
if(user){
return done(null, user);
}
});
}));
User model:
var userSchema = mongoose.Schema({
date : Date,
role : String,
newRole : { type: mongoose.Schema.Types.ObjectId, ref: 'newRole'},
authToken : { type: String, required : true, unique:true },
isAuthenticated : { type: Boolean, required : true },
username : String,
email : String,
password_first : String,
firstName : String,
lastName : String,
address : String,
phone : String,
resetPasswordToken : String,
resetPasswordExpires: Date });
Methods:
userSchema.methods.generateHash = function(password) {
return bcrypt.hashSync(password, bcrypt.genSaltSync(8), null);
};
userSchema.methods.validPassword = function(password) {
return bcrypt.compareSync(password, this.password_first);
};
var User = mongoose.model('User', userSchema);
module.exports = User;
And finally:
exports.changeByAdmin = function (req, res, next) {
User.findById({ _id : req.params.id }, function(err, updateUser) {
if(err) return next(err);
if (!updateUser) return next();
updateUser.email = req.body.email;
updateUser.firstName = req.body.firstName;
updateUser.lastName = req.body.lastName;
updateUser.address = req.body.address;
updateUser.phone = req.body.phone;
updateUser.password_first = updateUser.generateHash(req.body.password_first);
updateUser.save(function(err, updateUser) {
if(err) return next(err);
if(!updateUser) return next();
res.send({ success: true });
});
});
};
If I change only email of user, the user can login with new email and old password, but if I change password - user can't login. Please, advise the solution of this problem. Thank you.