Fix the Issue: multipart/form-data with Nested Objects

Content & configuration

Swagger/OpenAPI definition:

openapi: 3.0.0
paths:
 /api/test:
   post:
     operationId: TestController_test
     parameters: []
     requestBody:
       required: true
       content:
         multipart/form-data:
           schema:
             $ref: '#/components/schemas/TestDto'
         application/json:
           schema:
             $ref: '#/components/schemas/TestDto'
         application/x-www-form-urlencoded:
           schema:
             $ref: '#/components/schemas/TestDto'
     responses:
       '201':
         description: ''
         content:
           application/json:
             schema:
               $ref: '#/components/schemas/TestDto'
info:
 title: TESTAPI
 description: Routes description for test API
 version: '1.0'
 contact: {}
tags: []
servers: []
components:
 securitySchemes:
   bearer:
     scheme: bearer
     bearerFormat: JWT
     type: http
 schemas:
   BarDto:
     type: object
     properties:
       bar:
         type: string
     required:
       - bar
   FooDto:
     type: object
     properties:
       foo:
         type: string
       bar:
         $ref: '#/components/schemas/BarDto'
     required:
       - foo
       - bar
   TestDto:
     type: object
     properties:
       test:
         type: string
       foo:
         $ref: '#/components/schemas/FooDto'
     required:
       - test
       - foo

Is your feature request related to a problem?

When I attempt to send a multipart/form-request, it sends the nested object as string (JSON) instead of form-data. For example, when swagger describe the request using cURL, I encounter the following issue.

curl -X 'POST' \
  'http://localhost:3000/api/test' \
  -H 'accept: application/json' \
  -H 'Content-Type: multipart/form-data' \
  -F 'test=test' \
  -F 'foo={
  "foo": "string",
  "bar": {
    "bar": "string"
  }
}'

Describe the solution you'd like

I'd like to format the nested object in multipart/form-data as shown in this cURL request.

curl -X 'POST' \
  'http://localhost:3000/api/test' \
  -H 'accept: application/json' \
  -H 'Content-Type: multipart/form-data' \
  -F 'test=test' \
  -F 'foo[foo]=string' \
  -F 'foo[bar][bar]=string'

Describe alternatives you've considered

If the request is multipart/form-data and the data is in object format, we can format the nested object as follows.

Additional context

I believe there might be an issue. When I create an API and attempt to use multipart/form-data, the typical way to send data with tools like Postman or via Fetch/Axios involves a structure like 'foo[foo]...'. However, Swagger sends it in string (JSON) format, which doesn't work correctly in my application. I think it should be sent in the former format.

Start by reproducing the supplied OpenAPI definition in Swagger UI and inspect the generated multipart/form-data cURL request. The change is complete when nested objects are emitted with bracketed field names such as foo[foo] and foo[bar][bar], rather than as a JSON string.