integrate microsoft oauth2 client workflow

[yoshson]

Users from Microsoft Azure AD should be able to login via OAuth2 workflow.

[yoshson]

Add Microsoft OAuth2 Support

This PR introduces Microsoft OAuth2 authentication to django-authlib, enabling users to log in via Microsoft accounts (e.g., Outlook, Office 365, Azure AD).

Changes

1. New Module: Added authlib/microsoft.py with MicrosoftOAuth2Client class, supporting:

   • OAuth2 authorization flow via Microsoft Identity Platform (common tenant).
   • User data retrieval from Microsoft Graph API (mail and displayName).
   • Configurable via MICROSOFT_CLIENT_ID and MICROSOFT_CLIENT_SECRET settings.

2. Admin OAuth Support:

   • Extended authlib.admin_oauth to support Microsoft login for Django admin.
   • Added admin/__oauth_ms__/ endpoint and updated templates.

3. Frontend Integration:

   • Added Microsoft OAuth2 button to login templates.
   • Updated urls.py with /oauth/microsoft/ route.

4. Documentation:

   • Updated README.rst with Microsoft OAuth2 setup instructions.

5. Tests:

   • Added comprehensive test coverage for MicrosoftOAuth2Client in test_authlib.py.

Usage

from authlib.microsoft import MicrosoftOAuth2Client

urlpatterns = [
    path("oauth/microsoft/", views.oauth2, {"client_class": MicrosoftOAuth2Client}),
]

Add to settings.py:

MICROSOFT_CLIENT_ID = "your-client-id"
MICROSOFT_CLIENT_SECRET = "your-client-secret"