Add max-context-population input to override Azure PowerShell MaxCont…

[MaddyMicrosoft]

Summary

Adds a max-context-population input that exposes Azure PowerShell's existing Connect-AzAccount -MaxContextPopulation parameter through the action.

Fixes #606.

Problem

When enable-AzPSSession: true, the action calls Connect-AzAccount internally. Azure PowerShell loads a maximum of 25 subscription contexts by default (MaxContextPopulation = 25). When the authenticated identity can access more than 25 subscriptions, only a subset of contexts is loaded, so downstream cmdlets that enumerate or target other subscriptions (e.g. Get-AzSubscription followed by per-subscription calls) behave inconsistently. The only workaround today is to disable the PowerShell session and run Connect-AzAccount manually in a separate step, which platform teams have to roll out everywhere.

Change

• action.yml — new optional max-context-population input, no default.
• LoginConfig.ts — reads and trims the value; validate() rejects non-integer or out-of-range values (must be -1 or a positive integer) with a clear error, and warns when it's set without enable-AzPSSession (where it has no effect).
• AzPSScriptBuilder.ts — passes -MaxContextPopulation <value> to the invocation only when the input is set.
• AzPSLogin.ps1 — adds an [int]$MaxContextPopulation param, forwarded to Connect-AzAccount only when bound ($PSBoundParameters.ContainsKey).
• README.md — input-table row and a max-context-population section, including a note that -1 loads all contexts and can slow login for large tenants.
• Tests — cover the argument being passed when set and omitted when unset.

Backward compatibility

Fully backward-compatible. When the input is unset, -MaxContextPopulation is never passed and the Azure PowerShell default of 25 applies, so existing workflows are unaffected. The input only affects the enable-AzPSSession path; Azure CLI login is untouched.

Testing

• npm run build and npm test pass locally (33/33), including the PowerShell test that executes AzPSLogin.ps1 with the new parameter.
• Verified Connect-AzAccount exposes -MaxContextPopulation as an Int32 parameter (Az.Accounts).
• End-to-end validation of context loading against an identity with >25 subscriptions to be run via the release gate before merge.

Example

- uses: azure/login@v3
  with:
    client-id: ${{ vars.AZURE_CLIENT_ID }}
    tenant-id: ${{ vars.AZURE_TENANT_ID }}
    subscription-id: ${{ vars.AZURE_SUBSCRIPTION_ID }}
    enable-AzPSSession: true
    max-context-population: -1

[Copilot]

🟡 Changes recommended

The current max-context-population validation can accept formats/ranges that will fail or behave unexpectedly when bound to PowerShell’s Int32 parameter (e.g., 1e3 or out-of-range values).

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR exposes Azure PowerShell’s existing Connect-AzAccount -MaxContextPopulation knob via a new max-context-population action input, so large tenants (with >25 subscriptions) can reliably load more (or all) subscription contexts when enable-AzPSSession: true.

Changes:

• Added a new optional max-context-population input (documented in action.yml and README.md).
• Threaded the value through LoginConfig → AzPSScriptBuilder → AzPSLogin.ps1, applying it only when provided.
• Added unit tests to verify the argument is included when set and omitted when unset.

File summaries

File	Description
src/PowerShell/AzPSScriptBuilder.ts	Adds -MaxContextPopulation <value> to the PowerShell script invocation when configured.
src/PowerShell/AzPSLogin.ps1	Accepts MaxContextPopulation and forwards it to Connect-AzAccount only when bound.
src/common/LoginConfig.ts	Reads max-context-population input and validates it; warns when irrelevant (AzPSSession disabled).
README.md	Documents the new input, default behavior (25), and the -1 performance tradeoff.
action.yml	Declares the new max-context-population input and describes its semantics.
__tests__/PowerShell/AzPSScriptBuilder.test.ts	Adds coverage for passing/omitting -MaxContextPopulation.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 1
• Review effort level: Lite

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[Yeming Liu (isra-fel)]

Could use a label like "Available in v3" since we support two major versions concurrently - this could be a chance to promote v3

[Yeming Liu (isra-fel)]

LGTM but please check the inline comment and let me know what you think