Keep in mind that an app will require additional permissions beyond the default permission set in order to access content in the host web. This topic is discussed in Chapter 3. This current chapter will only discuss how to create a UI custom action that passes contextual information to a page supplied by the app. Chapter 3 also covers what’s required to actually use this information to call back into the SharePoint host environment.
App accessing content in the host site: Permissions will be needed. See Chapter 3
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