Soon, an improved version with enhanced security of Security & Encryption for Confluence Cloud will be released. Please check out next steps for administrators at this page.
Overview
When you create a Secret macro, it is automatically available as an entity for the whole space.
In other words, Secret macros belong to a space, and the page that you added the secret to is just a "location" where it is available.
When a secret is created, it is created as an entity for that specific space only.
This means you can copy a secret to multiple pages within a space.
Copying secrets to another space - secrets cannot be copied to pages located in other spaces, even if they reside on the same server.
Steps
Go to the page where the secret is located.
You can find out where a secret is located by referring to to Finding out where a secret is being used.
edit the page
select the secret macro
copy it (by pressing ctrl-c or command-c - Apple OS, or right-click → copy)
Navigate to to the page where the secret is to be copied to.
paste the secret (by pressing ctrl-v or command-v - Apple OS, or right-click → paste)
The new secret will also be associated with the new page.
If you use the Finding out where a secret is being used feature, you will see that the new page will be listed under Location.
