Response StatusCode 409 / User already exists

Hi,

In the protocol SCIM definition the following is stated in [paragraph 3.3](https://tools.ietf.org/html/rfc7644#section-3.3):

> If the service provider determines that the creation of the requested
> resource conflicts with existing resources (e.g., a "User" resource
> with a duplicate "userName"), the service provider MUST return HTTP
> status code 409 (Conflict) with a "scimType" error code of
> "uniqueness", as per Section 3.12.

When I look in the decompiled DLL "Microsoft.SystemForCrossDomainIdentityManagement.Service.dll" (with dotPeek) at `ControllerTemplate` I cannot find that statuscode 409 is returned when a user will be created, I cannot even find which exception I have to throw when a user (user with the same unique name) already exists.

Can SystemForCrossDomainIdentityManagement handle the response when the provider tries to create a user which already exists. If so which exception do I have to throw?
Do you know what Azure AD expect as response when a user already exists when creating a user?