OpenAPI parameter with brackets and variable name - openapi

Question

I am working on an API which allows searching with URLs like:
GET https://example.com/api/data?search[field1]=value1
GET https://example.com/api/data?search[field2]=value2
GET https://example.com/api/data?search[field1]=value1&search[field2]=value2
Basically, you can search for one or more field values by putting a field name in brackets. The problem is, the field names are defined by the user in their settings. The field name will be a string, but otherwise is not known ahead of time at a global level.
This answer is almost what I am looking to do, I just can't find a way to define the value inside the brackets to be "any string" rather than a list of known names.

Answer 1

The search parameter can be defined as a free-form object with the deepObject serialization style and minProperties: 1 to enforce the presence of at least one field in the search query.
Make sure you use OpenAPI 3.0 (openapi: 3.0.x) and not OpenAPI 2.0 (swagger: "2.0"); the latter does not support objects in query strings.
openapi: 3.0.2
...
paths:
/api/data:
get:
parameters:
- in: query
name: search
required: true
schema:
type: object
additionalProperties: true # Default value, may be omitted
minProperties: 1
# Optional example to use as a starting value for "try it out" in Swagger UI
example: >
{
"field1": "value1",
"field2": "value2"
}
style: deepObject
explode: true
responses:
200:
description: OK