Support a configurable or platform-appropriate location for .mg\mg.graphoptions.json

[btardif]

Microsoft Graph PowerShell currently stores Graph SDK options at:

%USERPROFILE%\.mg\mg.graphoptions.json

The location is hard-coded in Microsoft.Graph.Authentication:

GraphDirectoryPath = Path.Combine(
    Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
    ".mg");

GraphOptionsFilePath is then constructed beneath that directory.

Source references in tag v2.36.1:

• src/Authentication/Authentication.Core/Constants.cs
• src/Authentication/Authentication/Constants.cs
• src/Authentication/Authentication/Common/GraphSessionInitializer.cs
• src/Authentication/Authentication/Cmdlets/SetMgGraphOption.cs

This creates another tool-specific dot-directory directly under the user profile, with no documented environment variable or configuration setting for relocating it.

Environment

OS: Windows
Microsoft.Graph.Authentication: 2.36.1
Current path: %USERPROFILE%\.mg\mg.graphoptions.json

The file contains SDK configuration options such as:

DisableWAMForMSGraph
DisableLoginByWAM

No authentication-token relocation is being requested in this issue; the immediate request concerns configuration files such as mg.graphoptions.json.

Expected behavior

Provide a supported way to relocate Microsoft Graph PowerShell configuration.

Possible approaches:

1. Add an environment variable such as MSGRAPH_CONFIG_DIR.
2. Follow platform conventions by default:
   • Windows: %APPDATA%\Microsoft\GraphPowerShell
   • Linux/macOS: $XDG_CONFIG_HOME/microsoft-graph, falling back to ~/.config/microsoft-graph
3. Preserve the existing .mg location for backward compatibility and migrate or fall back to it when appropriate.

Motivation

A configurable location would:

• Avoid adding application-specific directories to the profile root.
• Support enterprise-managed and portable PowerShell environments.
• Improve separation between configuration, cache, authentication state, and user data.
• Allow consistent backup and profile-management policies.
• Better align with platform conventions and the XDG Base Directory specification.

Existing related issue

#747 — Consider moving graph cache from .graph to .cache/graph to match XDG specification remains open.

That issue addresses Graph cache placement. This request is narrower and complementary: it covers the hard-coded .mg configuration directory and mg.graphoptions.json.

Acceptance criteria

• A documented setting or environment variable controls the Graph PowerShell configuration directory.
• Get-MgGraphOption and Set-MgGraphOption use the configured location.
• Existing .mg configurations continue working through migration or backward-compatible fallback.
• Windows, Linux, and macOS path behavior is documented and tested.
• Configuration and cache locations can be controlled independently.