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I have shared a number of files located in my SP Online repository with a number of people outside of the company (mostly subcontractors and vendors). Each file was shared in a form of a link (File -> Share -> Anyone with a link). There are a lot of such files and links has been sent to multiple outside users.

Now I realize that even though there is still a need for the people to view the files, I am uncomfortable with the fact that anyone with a link can access corresponding file.

I could have re-shared the files anew using different settings but there are just too many of the files! Moreover, in doing so I might miss some of the people as files have not been shared in any centralized and controlled fashion (yes, I know...).

Is there any way (either through admin settings or PowerShell scripting) to add some kind of a filter on all outside/anonymous users that can access files shared with them using the "anyone with a link" function? Maybe using IP filtering or adding some kind of a page that requires entering a pass-code?

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You should be able to do this using the O365 content search and a bit of PowerShell:

  1. Get a list of all shared documents from content search or eDiscovery
  2. Iterate over this list and use the External Sharing API (CSOM) from PowerShell to un-share and re-share the documents

Content Search Is currently in beta, so you need preview permission to run it. You can access it here: https://protection.office.com/?ContentOnly=1#/contentsearchbeta

Search for all externally shared documents with this query: ViewableByExternalUsers:true AND ContentType:document

This returns everything shared externally, not only the anonymous links. So you have to filter these in PowerShell.

External Sharing API This is a client-side object model (CSOM) API, but it can also be called from PowerShell. You can Share and Unshare objects/documents with it.

Here is a good article explaining how the API works: https://blogs.msdn.microsoft.com/vesku/2015/10/02/external-sharing-api-for-sharepoint-and-onedrive-for-business/

And here is a good example of to use the API from PowerShell: https://drewmadelung.com/sharing-a-file-in-sharepoint-online-or-onedrive-with-powershell/

  • Could you clarify what profile/settings should I use to re-share the documents in order to implement an additional layer of end user identification that I am trying to implement? – David Bryant Jun 7 '18 at 7:48
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    To my knowledge you can currently only set the link expiration and read or read-write options for anonymous links as a limited protection for it. In the near future external sharing will be more flexible and work with other identity providers than Azure AD and reduce hopefully the need for anonymous sharing. – Bernd Rickenberg Jun 7 '18 at 13:28
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    An addition could be to monitor the actual usage of the anonymous links using the O365 audit log. It has data for the past three month showing every single access. I know it is not what you are asking but it might give a better picture of usages. – Bernd Rickenberg Jun 7 '18 at 13:59

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