->openapi->valid_input mangles headers

[tomascohen]

Just that, once you call it, headers get touched in bad ways :-D

[jhthorsen]

That is by design: Specifying a collectionFormat will turn the input data into an array. I think you might have been tricked by two things:

• The default collectionFormat is "csv" and not "multi".
• https://docs.mojolicious.org/Mojo/Headers#header returns join ", ", @$headers in case there are multiple values. (That should probably be documented though)

Also since a collectionFormat turns the string into an array, then you cannot validate the input twice.