def check_password_requirements(password: str) -> str:
    """Check if password meets requirements."""
    if len(password) < 8:
        return "Password must be at least 8 characters long."
    if not any(char.isdigit() for char in password):
        return "Password must contain at least one number."
    if not any(char.isupper() for char in password):
        return "Password must contain at least one uppercase letter."
    if not any(char.islower() for char in password):
        return "Password must contain at least one lowercase letter."
    return ""