How to get "oneOf" in OpenAPI output?

[bstro]

With the following Zod schema,

export const example = z.union([z.object({foo: z.object({…})}), z.object({bar: z.object({…})})])

I'm hoping to achieve the following OpenAPI output:

"oneOf": [
  {
    "type": "object",
    "properties": {
      "foo": {
        "type": "object",
        "properties": {…}        
      }
    }
  }, {
    "type": "object",
    "properties": {
      "bar": {
        "type": "object",
        "properties": {…}
      }
    }
  }
]

I can only seem to get zod-to-openapi to render to anyOf, but my API has a strict requirement that only one of the objects is passed.

Can anyone offer any pointers??