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Since current locator version (4/18/2019) does't support OAuth, which is used by the NetDocuments in order to authenticate users. All users are authenticated against Active Directory. After successful authentication the user email address and UPN are is matched with user names email addresses in the NetDocuments system.
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User id and groups id are used as an identification tokens in the following format:
SID Scope: NetDocuments+ClientId
SID: User id or group id
Example: NetDocumentsSomeClinetId\\userId