How should user accounts be stored in MongoDB?

Store each account as a document with at least login and hash, backed by a unique index on login.

const users = db.collection('users');
await users.createIndex({ 'login': 1 }, { unique: true });

Document structure:

{
  login: "anna",
  hash: "$2y$10$bsD5ralzGlwENSF1JY3..."
}

The unique index:

• Prevents duplicate usernames
• Speeds up login queries
• Returns error on duplicate insert