How can I use cloud identity proxies to provide secure access to my legacy on-premises web applications?

We ask the same underlying question in different ways.

• How can I use cloud identity proxies to provide secure access to my legacy on-premises web applications?
• I need to secure my legacy on-premises web applications. What is the process for using cloud identity proxies to achieve this?
• How do cloud identity proxies function when you are trying to secure access to older, on-premises web applications?