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The accounts in your azure tenant will be authenticated through the azure active directory application you have just created. If you click the Users tab on the portal menu, you will see the users in your tenant. The users in this list that are Salesforce users and have access to S-Drive are the ones you can Enable for Content Authoring in S-Drive in the next step.
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If you want to access an external user to use Edit Online, you should click the New guest user button and fill in the user’s information. After they confirm the request you sent, they will be able to access Edit Online with that account.
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