[BUG] [Feign] Incorrect generated format with Content-Type: application/x-www-form-urlencoded

Description

Hi, we are trying to genenerate an feign client to call an Oauth2 token method. In curl, this call is like this:

curl --request POST \
  --url https://xxxxxxxxxxxxxx/oauth2/v1/token \
  --header 'Authorization: Basic XXXXXXXX' \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --header 'User-Agent: insomnia/9.3.2' \
  --data username=XXXXX \
  --data password=XXXXX \
  --data grant_type=password \
  --data scope=XXXXXXXXXXX/super_scope+offline_access 

but when we run the openapi generator, feign is doing this call:

https://xxxxxxxxx/oauth2/v1/token?username=XXXXXX&password=XXXXX&grant_type=password&scope=XXXXX/super_scope+offline_access'

that retuns a bad request exception

openapi-generator version

3.0.1

OpenAPI declaration file content or url

/token:
post:
tags:
- "Oauth2"
summary: "Generate new access and refresh token"
description: ""
operationId: "token"
parameters:
- in: "header"
name: "Authorization"
description: "Basic authentication"
required: true
schema:
type: string
requestBody:
description: Session credentials
content:
application/x-www-form-urlencoded:
schema:
$ref: "#/components/schemas/TokenRequest"
responses:
"200":
description: "Successful operation"
content:
application/json:
schema:
title: "TokenResponse"
oneOf:
- $ref: "#/components/schemas/OauthSuccess"
- $ref: "#/components/schemas/OauthError"
"400":
description: "Bad request"
content:
application/json:
schema:
$ref: "#/components/schemas/OauthError"
"401":
description: "Forbidden"
content:
application/json:
schema:
$ref: "#/components/schemas/OauthError"

Can help me to try to generate the request so that the parameters appear in the body and not in the URL?

Start with the Feign generator's handling of the supplied application/x-www-form-urlencoded requestBody and compare the generated request with the OpenAPI declaration. Reproduce the token operation, then verify that username, password, grant_type, and scope are encoded in the request body rather than appended to the URL.