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Feature #1: Implementing Account Sign Up
Feature #2: Associating accounts with their owners
Feature #3: Add subdomains to accounts
Feature #4: Ensuring unique subdomain
Feature #5: Restricting subdomain names
Feature #6: Preventing invalid subdomain names
Feature #7: Testing subdomain authentication
Feature #8: Invalid usernames or passwords
Feature #9: Restricting sign in by account
Feature #10: Handling user signup