Add Support for Authorization Code Flow Authentication

[Mister-Joe]

Overview

The Get-GraphTokens function currently only supports device code flow for authentication. This can be problematic when an Entra ID tenant has blocked device code flow via a conditional access policy. This PR adds support for authorization code flow, allowing users to choose between device code flow (default) or authorization code flow (Get-GraphTokens -AuthorizationCodeFlow).

How does it work?

A browser is opened and a request is made to the /organizations/oauth2/v2.0/authorize endpoint. The user is prompted to authenticate. If authentication is successful, the browser is redirected to an HttpListener on localhost where the authorization code is captured.

This authorization code is then exchanged in a request to the /organizations/oauth2/v2.0/token endpoint for an access token and FOCI refresh token for the Azure CLI client, which in turn is exchanged in another request to the /organizations/oauth2/v2.0/token endpoint for an access token and refresh token for the Microsoft Office client.

Usage

1. Get-GraphTokens -AuthorizationCodeFlow

2. In the browser window that opens, select your account and authenticate.

3. Return to your CLI and note that you now have tokens for the correct resource, client, and scopes.