I'm slightly confused. Where are you surfacing their task they are having to approve?

 

When using SharePoint and Nitnex in O365, the user has to be logged in "Authenticated" in order to interact with the task and the SharePoint list. Are you doing something through an anonymous form?

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I'm slightly confused. Where are you surfacing their task they are having to approve?

 

When using SharePoint and Nitnex in O365, the user has to be logged in "Authenticated" in order to interact with the task and the SharePoint list. Are you doing something through an anonymous form?

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They have a requirement to be prompted for Authentication to verify that the user approving the task is the user at the point of approval. Personally I agree with yourself where they user is already authenticated if they even get to the task however that isn't enough to satisfy the requirement.

They do have something similar working for the On Premises version of Nintex, which is a WSP Solution file that adds additional options to Nintex tasks as described here:
https://community.nintex.com/t5/Nintex-for-SharePoint/21CFR-Part-11-Compliance-re-authenticates-user-in-order-to/td-p/50991

But there is no equivalent for Nintex 365SharePoint Online

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