fix: make signin email case-insensitive

Closes #3981

src/app/api/users/route.ts

@@ -1,11 +1,11 @@
-import { z } from 'zod';
-import { ROLES } from '@/lib/constants';
-import { uuid } from '@/lib/crypto';
-import { hashPassword } from '@/lib/password';
-import { parseRequest } from '@/lib/request';
-import { badRequest, json, unauthorized } from '@/lib/response';
-import { canCreateUser } from '@/permissions';
-import { createUser, getUserByUsername } from '@/queries/prisma';
+import { z } from "zod";
+import { ROLES } from "@/lib/constants";
+import { uuid } from "@/lib/crypto";
+import { hashPassword } from "@/lib/password";
+import { parseRequest } from "@/lib/request";
+import { badRequest, json, unauthorized } from "@/lib/response";
+import { canCreateUser } from "@/permissions";
+import { createUser, getUserByUsername } from "@/queries/prisma";
 
 export async function POST(request: Request) {
   const schema = z.object({
@@ -27,15 +27,17 @@ export async function POST(request: Request) {
 
   const { id, username, password, role } = body;
 
-  const existingUser = await getUserByUsername(username, { showDeleted: true });
+  const existingUser = await getUserByUsername(username, {
+    showDeleted: true,
+  });
 
   if (existingUser) {
-    return badRequest({ message: 'User already exists' });
+    return badRequest({ message: "User already exists" });
   }
 
   const user = await createUser({
     id: id || uuid(),
-    username,
+    username: username.toLowerCase(),
     password: hashPassword(password),
     role: role ?? ROLES.user,
   });