After familiarizing ourselves with the essential building blocks of a well-structured Streamlit web application, we now require an additional feature to deploy a production-ready app: a secure user authentication service. Once all users requesting access to the application are authenticated, we can ensure a secure user experience where private data remains safe and any unwelcome or malicious requests are effectively denied. In this chapter, we will learn how to establish user accounts, verify user actions, and implement other housekeeping measures expected of any proficient software engineer.