add AKSHTTPCustomFeatures header decorator for creating aks

[yangzuo0621]

This change adds customized headers decorator by passing environment, which let users use preview features when creating AKS cluster.

[tombuildsstuff]

hi @yangzuo0621

Thanks for this PR.

Taking a look through here unfortunately this isn't something we can ship in Terraform at this time for a number of reasons.

The primary one here is that these are sourced from an Environment Variable and thus aren't defined in the config - however even if we were to move these to schema fields, at this point in time these can only be set in/parsed from the HTTP Headers for the request/response.

Whilst this approach works insofar as it sends the headers, due to the volatility of the Azure API's there's no guarantee this won't change behaviourally between different versions of the Azure API - and since this isn't provided in the Azure SDK (or the Swagger which supports it) - in practice it'd be hard for us to detect that this functionality has changed.

In order to support this functionality (and implement #6793) we'd need these Headers to be added to the Swagger for the AKS API - at which point this'll become available in the Azure SDK (and any other tooling which uses it). Whilst that may seem like a small distinction - that means this functionality becomes covered by the ARM Deprecation policy - meaning that changes have to go through a deprecation policy such that external tooling can rely on it. In order to get that added I'd suggest opening an issue on the AKS Repository where someone from the AKS Team should be able to get that added to the next version of the Swagger, which'd allow us to support this functionality.

As such whilst I'd like to thank you for this contribution, until this information is exposed in the Azure Swagger (such that there's a compatibility guarantee) I'm going to have to close this PR for the moment.

Thanks!

[dhirschfeld]

Hi @tombuildsstuff, whilst I'm fine with the wontfix resolution and the reasons for it, it seems you could have mentioned that over in #6793? It feels like I've been wasting the last 18 months monitoring an issue that won't be fixed when I should have instead opened an issue in Azure/AKS 🙁

Ad-hoc terraform users obviously aren't the best placed to open an issue in Azure/AKS as they have no insight into what other mechanism the azurerm provider might be able to support to provide access to preview features.

Instead of simply closing this as wontfix it would be great if someone from the azurerm team could open the issue in Azure/AKS on behalf of users, requesting a different mechanism for preview features that would be supportable by the azurerm provider.

[github-actions]

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