[Zope] how to set value of hidden form field by a cookie

[prabuddha ray]

I've to set the value of a hidden form field by a cookie value.

e.g; invalidval request/cookies/login|nothing;
 i tried this :
<input name="invalid" type="hidden" value="string: ${invalidval}">
and also this 
<input name="invalid" type="hidden" tal:attributes="value invalidval">

but it is rendering the text in quotes directly.
what is the correct way.

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