[FEATURE] Request: M365 Connector — Cross-Tenant Graph API Support (Azure B2B)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The M365 connector only queries the authenticated user's home tenant. Users with Azure B2B guest access to other tenants get empty results from sharepoint_search / sharepoint_folder_search for guest-tenant content, even with explicit permissions (e.g., SharePoint Site Owner) on the target site. The connector's access tokens are bound to the home tenant, so cross-tenant Graph API queries are never issued.

Proposed Solution

1. During authentication or in connector settings, enumerate the user's guest tenancies (e.g., via GET /v1.0/me/memberOf or listing multi-tenant identities)
2. Let users select which tenants to include in search scope
3. Acquire guest-tenant-scoped tokens via https://login.microsoftonline.com/{guestTenantId}/oauth2/v2.0/token (standard OAuth OBO / B2B flow)
4. Issue Graph search calls against each authorized tenant

Reference: Microsoft Entra B2B overview

Alternative Solutions

• Minimal implementation: A configuration field where users manually enter additional tenant IDs to query, skipping auto-discovery.
• Current workaround: Using Claude in Chrome to access cross-tenant SharePoint via the browser session. This works but requires an active tab, doesn't integrate with Enterprise Search, and can't be used for background queries.

Priority

Critical - Blocking my work

Feature Category

Other

Use Case Example

• A nonprofit hires an external entity so they live across two M365 tenants. Claude runs through Tenant B, but the team's knowledge base (SharePoint Wiki) lives in Tenant A. The user has B2B guest access with Site Owner rights, but the connector can't see any Tenant A content.
• A consultant with their own M365 tenant has guest access to three client tenants. They want to use Enterprise Search to query documents across all four tenants.
• A parent company wants Claude to search SharePoint sites across subsidiary tenants where employees have been added as B2B guests.

Additional Context

• Multi-tenant M365 setups are common in nonprofits, holding structures, and consulting firms — exactly the organizations adopting Claude Team/Enterprise plans.
• Microsoft Graph API fully supports this pattern. The technical lift is token acquisition per guest tenant and parallel/sequential search calls.
• The M365 Connector Security Guide confirms that tenant isolation is currently enforced via cryptographically signed access tokens bound to a single tenant.