use mydatabase
db.createUser(
  {
    user: "myreaduser",
    pwd: "password",
    roles: [{role: "read", db: "mydatabase"}]
  }
)

E QUERY    [thread1] Error: Authentication failed. :
DB.prototype._authOrThrow@src/mongo/shell/db.js:1461:20
@(auth):6:1
@(auth):1:2
exception: login failed