OpenAPI to define optional parameters with undefined names

Question

Simple question: How do you write an OpenAPI spec. that accepts optional parameters with undefined names (i.e. the parameter names can be any random string)?

Example:

GET /api/someEndPoint
GET /api/someEndPoint?key1=value1&key2=value2&key3=value3
GET /api/someEndPoint?aaa=valueA

/api/someEndPoint:
  get:
    parameters:
      - description: one or more key value pairs
        name: ???
        in: query
        required: false
        schema:
          type: string