Request validation does not work correctly with "additionalProperties: false"

[evgenykireev]

Background

OpenAPI v3 defines additionalProperties attribute as
Value can be boolean or object. Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema. Consistent with JSON Schema, additionalProperties defaults to true.

Problem

additionalProperties: false is not taken into account when validating JSON - a payload with attributes that are not listed in schema will still be valid.
It only happens when additionalProperties is declared inside anyOf / allOf block

Steps to reproduce

package main

import (
	"encoding/json"
	"fmt"

	"github.com/getkin/kin-openapi/openapi3"
)

func main() {
	payload := map[string]interface{}{
		"prop1": "val",
		"prop3": "val",
	}

	schemas := []string{`
{
	"type": "object",
	"additionalProperties": false,
	"required": ["prop1"],
	"properties": {
		"prop1": {
			"type": "string"
		}
	}
}`, `{
	"anyOf": [
		{
			"type": "object",
			"additionalProperties": false,
			"required": ["prop1"],
			"properties": {
				"prop1": {
					"type": "string"
				}
			}
		},
		{
			"type": "object",
			"additionalProperties": false,
			"properties": {
				"prop2": {
					"type": "string"
				}
			}
		}
	],
}
`}

	for _, jsonSchema := range schemas {
		var dataSchema openapi3.Schema
		json.Unmarshal([]byte(jsonSchema), &dataSchema)
		err := dataSchema.VisitJSON(payload)
		fmt.Println("err", err)
	}
}

Result

• first test will fail with "Property 'prop3' is unsupported" (correct)
• second test will pass (incorrect)