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As with most vendor documentation, they are inaccurate regarding this piece. They do require a NameID and it's the basis of an auto-generated username value in the user pool. It does not have to be any particular Format, and they mis-speak by suggesting you should use "persistent". You certainly can, but you would need to understand that they'll be visible in the pool and of course it means correlation between pools would not be easy to dopossible. That may be good or bad, it just depends on your needs. If you want to use a more globally consistent value, you can, just pick a different Format.
Whatever you use, it will construct the eventual username key based on combining the IdP "name" with the NameID value with an underscore in between them. So it essentially auto-scopes the value with a prefix.
Having settled on a Format, make sure you add that to the Cognito metadata in a <md:NameIDFormat> element to trigger its use.
Attribute Requirements
Cognito essentially acts like a simplistic kind of user directory, and it supports a number of pre-defined attributes and allows custom fields to be created. A subset of them can be marked as "required" when the pool is created, but not changed afterward.
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