[BUG] Authorization Header; Case is not respected

Created by: RalphBragg

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
Have you validated the input using an OpenAPI validator (example)?
What's the version of OpenAPI Generator used? Latest Master
Have you search for related issues/PRs? Yes
What's the actual output vs expected output? Header is accepted with a capitilsation
[Optional] Bounty to sponsor the fix (example)

Description

An OAuth 2.0 Access Token is conveyed in a header called Authorization. This can be defined for example like below. - description: 'An Authorisation Token as per https://tools.ietf.org/html/rfc6750' explode: false in: header name: Authorization required: true schema: type: string style: simple

Unfortunately the capitalization requirements of the Authorization header isn't being respected by the generator

{ "error": [ { "path": ".headers.authorization", "message": "should have required property 'authorization'", "errorCode": "required.openapi.validation" } ] }

So a request with Authorization results in an error being thrown.

openapi-generator version

Latest, it is not a regression.

OpenAPI declaration file content or url

        - description: 'An Authorisation Token as per https://tools.ietf.org/html/rfc6750'
          explode: false
          in: header
          name: Authorization
          required: true
          schema:
            type: string
          style: simple

Command line used for generation

openapi-generator generate -g nodejs-express-server -i account-info-openapi.yaml

Steps to reproduce

Generate the server, launch server, send a request with an Authorization header with a capital A.