Azure APIM validate-content is not validating as expected for JSON - azure-api-management

Question

I had an issue with validate-content policy our API, so for sharing in public
I created a simple Open API Spec yaml file with a schema to create an API and then added validate-content policy. It's validating as expected when a JSON when the right JSON is sent or if I miss any required fields it's preventing with right validation error. However when I send a completely unrelated JSON it's going through fine, expectation is to prevent otherwise it will break the policy expressions.
As suggested in one of the other threads, I also tried adding request representation and specified message schema but behaviour is same.
I also verified it on https://www.jsonschemavalidator.net/, where validation is as expected
I am not sure it's ignoring as a fact that JSON validation ignores extra elements
Contents of the YAML used
openapi: "3.0.0"
info:
title: address-schema-validation
description: This is a loop back API to test schema validation
version: '1.0'
license:
name: MIT
paths:
/validate:
post:
summary: Submit a request for validation
operationId: validate
requestBody:
content:
application/json:
schema:
$ref: "#/components/schemas/AddressBody"
responses:
'200':
description: valid payload
content:
application/json:
schema:
$ref: "#/components/schemas/AddressBody"
components:
schemas:
AddressBody:
type: object
properties:
address:
type: string
example: "01 Auckland"
name:
type: object
required:
- fistName
- lastName
properties:
fistName:
type: string
example: Fist Name
lastName:
type: string
example: Last Name
Policy
<policies>
<inbound>
<base />
<validate-content unspecified-content-type-action="prevent" max-size="102400" size-exceeded-action="prevent" errors-variable-name="requestBodyValidation">
<content type="application/json" validate-as="json" action="prevent" />
</validate-content>
<return-response>
<set-status code="200" reason="OK" />
<set-header name="Content-Type" exists-action="override">
<value>application/json</value>
</set-header>
<set-body>#(context.Request.Body.As<String>())</set-body>
</return-response>
</inbound>
<backend>
<base />
</backend>
<outbound>
<base />
</outbound>
<on-error>
<base />
</on-error>
</policies>
JSON that picks up the validation error
{
"address": "01 Auckland",
"name": {
"fistName1": "Fist Name",
"lastName": "Last Name"
}
}
with error message
{
"statusCode": 400,
"message": "Body of the request does not conform to the definition which is associated with the content type application/json. Required properties are missing from object: fistName. Line: 6, Position: 5"
}
The following JSON is expected to be prevented but it's not
{"prevent":"me"}

Answer 1

In fact validation is being done as expected, to prevent unexpected JSON, the schema should have a required root element, if the root element is optional then when completely unrelated JSON is posted the validation policy will simply ignore the unexpected elements.