Write a user validation function
Level: Intermediate (score: 3)
Create a function that takes a username and checks for a valid user:
1. The username is in USERS
2. The user's account has not expired.
3. The user has the ADMIN role.
If those 3 conditions are met return SECRET.
If one of the conditions is not True, raise an appropriate exception:
- UserDoesNotExist
- UserAccessExpired
- UserNoPermission
Remember to look at the tests for more details. Have fun, keep calm, and code in Python!