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More information about this here https://www.atlassian.com/blog/announcements/forge-launch
So why do other apps on the marketplace not require “Allow access”?
Other apps built using Atlassian Connect store customer data on their servers in the ‘public cloud.' Even so, users of these apps are not informed about this in the same way as users of apps build on Atlassian Forge are:
“share data with 1 domain outside of Atlassian”
Furthermore, individual users don’t have to accept sharing data with domains outside of Atlassian, even though most, if not all Atlassian Connect apps do.
The good thing is Atlassian is strengthening the security profile of all apps and will eventually unify Atlassian Connect and Forge apps and have them comply with the same strict security policies.