I've just used 'candidate' attributively to mean '[worth considering as] a real possibility [for the purpose stated, or implied by context] (eg a candidate term or construction).
I've not been able to find a licensing of any attributive usage in AHDEL, Collins, M-W, RHK Webster's or Google Dictionary.
YourDictionary merely lists variously sourced examples of the usage meaning 'relating to / worthy of a candidate':
As soon as Jake Weller left, Cynthia questioned her husband about the candidate filing papers Weller handed him.
Dean pulled down the top on his Jeep and slowly drove uptown, giving off what he hoped were candidate smiles and waves to the locals, all of whom seemed to be walking the sun drenched street.
I have found one incidental example of the 'obviously should be at least considered as a possibility' sense within Wiktionary Talk:
WT:CFI does not define "attributive". If you have your own candidate definition of "attributive" ...
But is such a usage acceptable?