#2, добавила модель юзера

models/User.js

+const mongoose = require("mongoose");
+const bcrypt = require("bcrypt");
+const {nanoid} = require("nanoid");
+const Schema = mongoose.Schema;
+const SALT_WORK_FACTOR = 10;
+
+const UserSchema = new Schema({
+  username: {
+    type: String,
+    required: true,
+    unique: true,
+    validate: {
+      validator: async function(value) {
+        if (!this.isModified("username")) return;
+        const user = await User.findOne({username: value});
+        if (user) return false;
+      },
+      message: props => `Username ${props.value} is already exists`
+    }
+  },
+  password: {
+    type: String,
+    required: true
+  },
+  displayName: {
+    type: String,
+    required: true
+  },
+  phone: {
+    type: String,
+    required: true
+  },
+  token: String
+});
+
+UserSchema.pre("save", async function (next) {
+  if (!this.isModified("password")) next();
+
+  const salt = await bcrypt.genSalt(SALT_WORK_FACTOR);
+  this.password = await bcrypt.hash(this.password, salt);
+  next();
+});
+
+UserSchema.set("toJSON", {
+  transform: (doc, ret) => {
+    delete ret.password;
+    return ret;
+  }
+});
+
+UserSchema.methods.checkPassword = function(password) {
+  return bcrypt.compare(password, this.password);
+};
+UserSchema.methods.generateToken = function() {
+  this.token = nanoid();
+};
+
+const User = mongoose.model("User", UserSchema);
+
+module.exports = User;