upd

server/src/models/User.ts

@@ -6,6 +6,8 @@ const userSchema = new Schema(
       type: String,
       required: true,
       unique: true,
+      trim: true,
+      lowercase: true,
     },
     password: {
       type: String,

server/src/routes/login.ts

@@ -8,13 +8,16 @@ import { createSecretKey } from "crypto";
 const router = Router();
 
 router.post("/", async (req, res) => {
-  const { username, password } = req.body;
+  const username = req.body.username.toLowerCase().trim();
+  const { password } = req.body;
 
   if (!username || !password) {
     return res.json({ error: "Неверный логин или пароль" });
   }
 
-  const user = await User.findOne({ username }).lean();
+  const user = await User.findOne({
+    username: { $regex: new RegExp(username, "i") },
+  }).lean();
 
   if (!user) {
     return res.json({ error: "Неверный логин или пароль" });