TransformAttributeResolver adds instead of replacing values

[Kimmo Koivisto]

>* Peter Schober <peter.schober at univie.ac.at> [2021-09-07 14:59]:
>> > If not possible, is there any way one could convert multivalue
>> > attribute to single value to fix this?
>>
>> How should the software know which value you'd like to keep?
>
>The only way I can think that doesn't rely on any code of your own
>would be using the SP's REMOTE_USER precedence list feature.
>
> ...

REMOTE_USER is already in use.

My use case is that our application is able to use only nationalIdentificationNumber attribute. Some IdP's provide social security number in nationalIdentificationNumber, some in schacPersonalUniqueID and some IdP's might provide both attributes.
I'm trying to figure out the solution for this use case but seems to be that I'm out of luck.

Tried also Template resolver but it also only adds if attribute exists:

<AttributeResolver type="Transform" source="schacPersonalUniqueID">
 <Regex match="^.*:(.*)$">$1</Regex>
</AttributeResolver>

<AttributeResolver type="Template" sources="schacPersonalUniqueID" dest="nationalIdentificationNumber">
 <Template>$schacPersonalUniqueID</Template>
</AttributeResolver>

>Maybe submit a feature request for the Transform resolver to be
>replacing values.
>-peter

Thanks you for the help, this helped me to understand AttributeResolver better and maybe I need to accept the fact that all scenarios will not work.
Cheers,
Kimmo