nameID content vs format

[Cantor, Scott]

The IdP would never produce a transient Format that was anything but transient unless it was misconfigured, and that is definitely a MUST NOT.

If you want to pass them an email address, you would use that Format.

If you want to pass them eduPersonUniqueID, that's typically an Attribute, and the convention for expressing any Attribute as a NameID (assuming it's sensible to do so) is that the Format is set to the Attribute's Name. I do it all the time, mostly with employeeNumber and one or two locally-defined ones.

-- Scott