Fix StorageAccountConfig.Key to return account key instead of connection string

[Copilot]

This PR closes #

The changes in this PR are as follows:

• Added AccountKey member returning just the storage account key via listKeys(...).keys[0].value
• Added ConnectionString member explicitly returning the full connection string
• Marked Key member as obsolete - it incorrectly returned a connection string despite its name suggesting it returns just the key
• Updated all internal usages (tests, samples, builders) from .Key to .ConnectionString
• Updated storage account API version from 2017-10-01 to 2025-06-01 to match the current storage account resource API version

I have read the contributing guidelines and have completed the following:

• Tested my code end-to-end against a live Azure subscription.
• Updated the documentation in the docs folder for the affected changes.
• Written unit tests against the modified code that I have made.
• Updated the release notes with a new entry for this PR.
• Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Did not test against live Azure subscription - changes are purely syntactic (adding new members and deprecating existing one). The obsolete member maintains identical behavior for backward compatibility.

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

open Farmer
open Farmer.Builders

let storage = storageAccount { name "mystorage" }

let webApp = webApp {
    name "myapp"
    // Use ConnectionString for connection strings
    setting "STORAGE_CONN" storage.ConnectionString
    // Use AccountKey when you need just the key
    setting "STORAGE_KEY" storage.AccountKey
}

arm {
    location Location.WestUS
    add_resources [ storage; webApp ]
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>StorageAccountConfig.Key should return the key but returns full connection string</issue_title>
<issue_description>From the source code:

type StorageAccountConfig = { 
... 
} with

    /// Gets the ARM expression path to the key of this storage account.
    member this.Key = StorageAccount.getConnectionString (this.Name)

Maybe this one should be obsoleted, a new property AccountKey exposed returning just the key, and connection string can either be acquired by using StorageAccount.getConnectionString or another property ConnectionString is added.</issue_description>

<agent_instructions>Make a non-breaking fix for member this.Key (such as this.AccountKey), add a new member for getting the connection string, and mark the old member as obsolete with a message on the proper member to use instead..</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes StorageAccountConfig.Key should return the key but returns full connection string #1238

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[ninjarobot]

This is a super-old API version @copilot. I don't think it's changed, and this likely still works, but stick with the same version used when deploying storage accounts. At this time, that is 2025-06-01.

[Copilot]

Updated to use API version '2025-06-01' to match the storage account resource version. Changes applied in commit f5b2f39.