How to set addtionalProperties via OpenAPI 3.0 Java annotations?

Question

My end goal is to simply have some generated OAS 3.0 documentation contain the size constraints on a Map<String, String> 's keys and values. This code will be in Kotlin, but it shouldn't muddle the example too much:

    @RouterOperation(
        operation = Operation(operationId = ":POST/foo/bar",
            requestBody = RequestBody(
                content = [Content(
                    mediaType = MediaType.APPLICATION_JSON_VALUE,
                    schema = Schema(implementation = MyRequestData::class)
                )]
            )
        )
    )
    suspend fun myHandler(@Valid request: Request, @Valid data: MyRequestData) {}

//
// and
//

    @Serializable
    data class MyRequestData(
        @field:Valid
        @field:Schema(description = "A map")
        val someKeysToValues: Map<
                @Size(max = 100) String,
                @Size(max = 50) String>? = null

        @field:Valid
        @field:ArraySchema(schema = Schema(description = "A list item"))
        val someOtherKeys: List<@Size(max = 100) String>? = null,
    )

I am having a bear of time trying to figure out how to add in the key & value constraint information to the generated swagger json for the map. According to the documentation I should be using additionalProperties ... but my only options in a @Schema are to turn it to true or false.

1. For a generic list it was easy enough to just use @ArraySchema, but nothing like that exists for Maps
2. Unfortunately, the constraint annotations are not auto-detected & filled in like they were when using @ArraySchema either
3. I've tried setting additionalPropertiesSchema to an object with @Schema and/or @SchemaProperty annotations, but it appears to do nothing
4. I haven't found anything like @AdditonalSchemaProperty or @SchemaAdditionalProperty or similar to just add on top

I feel like I must be missing something incredibly obvious. At the moment, this the UI output I wind up getting:

MyRequestData{
  someKeysToValues {
    description:   A map
    < * >:    string
              A map

  }
  someOtherKeys  [
    string
    maxLength: 100
    minLength: 0
    A list item
  ]
}

I cannot seem to figure out how to get to that inner schema to add in max-length information. Any tips or examples?

Notes:

• This is being included via org.springdoc:springdoc-openapi-starter-webflux-ui but the annotations & functionality here appears to be just from io.swagger.core.v3:swagger-annotations-jarakata (2.2.15)