Giving an AI assistant read-only access to Microsoft Loop — without breaking permissions

Giving an AI assistant read-only access to Microsoft Loop — without breaking permissions I wanted my AI assistant to read my team's Microsoft Loop pages — summarize a workspace, pull the latest OKRs into a draft, answer "what did we decide about X." Simple ask. It turned into a genuinely interesting engineering problem, and I ended up building a small open-source MCP server to solve it. Here's the challenge, the solution, and the traps along the way. The result is open source (MIT): loop-reader-mcp. The challenge Two walls, right at the start. Wall 1: Microsoft Loop has no content API. As of mid-2026, there's no Graph endpoint to read or write a Loop page's content — no "get page," no "list workspace." Loop is positioned against Notion and Confluence, but you can't programmatically get your own content out in a structured way. The 2026 Loop roadmap is about governance, not a content API. Wall 2: where Loop actually stores things. Loop workspace pages live in SharePoint Embedded (SPE) containers, and Loop components from Teams/Outlook live as .loop files in OneDrive. There is a documented trick: Microsoft Graph can convert a .loop file to HTML on the fly with GET /drives/{id}/items/{id}/content?format=html. So reading is possible through the file layer even without a Loop API. But then the real problem showed up — the one worth writing about. The permission trap SharePoint Embedded does not accept delegated (per-user) tokens for content downloads. Only an app-only identity can fetch the bytes. If you build the naive thing — a service that uses its app identity to read Loop — you've created a permission-flattening machine. The app can read everything, so anyone who can talk to your service can read any Loop page in the tenant, regardless of what they personally have access to. That's a data leak with extra steps. Unacceptable. So the question became: how do you let a service read content with an app identity, while guaranteeing each user only sees what they're allowed to see? The solution: split discovery from retrieval The insight that cracked it: Graph Search is security-trimmed for delegated callers, even for SPE content. Search respects the user's permissions; only the content download needs the app identity. So I split the two operations across two identities: Discovery runs as the user. When the assistant searches Loop, the server exchanges the user's token via the OAuth On-Behalf-Of (OBO) flow and calls Graph Search as that user. Microsoft trims the results to exactly what they can access. The server records the (driveId, itemId) of every hit in a short-lived, per-user cache. Retrieval is gated by that discovery. When the assistant asks to read a page, the server refuses unless that exact (driveId, itemId) pair is in this user's cache — i.e. unless they personally just discovered it via their own trimmed search. Only then does it use the app identity to fetch and convert the bytes. search -- OBO (user identity) --> Graph Search -> results trimmed by Microsoft -> (driveId,itemId) cached per user read -- is this pair in the caller's cache? --> no -> refuse (no Graph call) yes -> app identity -> ?format=html Enter fullscreen mode Exit fullscreen mode The authorization decision is Microsoft's, not mine. A user can't discover a page they can't access (search runs as them), and can't read a page they didn't discover. The app identity is just a retrieval mechanism for bytes the user already proved they can see. Permission flattening solved. Making it a proper MCP server I exposed this as a remote Model Context Protocol server with three read-only tools: loop_search, loop_list_components, and loop_get_page. Read-only isn't a policy toggle — the Graph client only permits GET and POST /search/query, so there's structurally no way to write. (Good, because overwriting a .loop file with anything else corrupts it, and there's no supported write API anyway.) For auth, I initially tried to put a platform "easy auth" gateway in front of the server. Big mistake — the gateway intercepted the OAuth handshake and the MCP client could never discover where to log in. The fix was to make the server its own OAuth resource server: it publishes the discovery documents (/.well-known/oauth-protected-resource and /.well-known/oauth-authorization-server) pointing clients at Microsoft Entra, and it validates the incoming token itself (signature via Entra's JWKS, audience, issuer, expiry). No gateway, no interception, and access is still fully gated because Entra only issues tokens to users assigned to the app. Lessons learned (the un-glamorous half) Delegated search + app-only retrieval is a legitimate, powerful pattern for any service sitting on top of SharePoint Embedded. Trim on discovery, fetch on retrieval. Don't let a platform auth gateway wrap a remote MCP server — the MCP OAuth flow needs the client to reach the server's own discovery/challenge. Let the app own auth. Bind the retrieval gate to (driveId, itemId) pairs, not just the item ID — otherwise a caller could replay a discovered ID against a different drive. Fail closed everywhere: no token, no identity, cache miss, expired entry -> refuse. On multi-instance hosting a user just re-searches; that's a safe failure, not a leak. The app credential is the crown jewel. It holds tenant-wide read. Store it in a secrets manager, prefer a certificate, rotate it, and consider IP-allowlisting the server. Watch the revocation lag. Discovery results are cached for a few minutes, so losing access isn't instant. Tune the TTL to your risk tolerance. Try it The code is on GitHub under MIT: github.com/DenizV/loop-reader-mcp. The README covers the Entra app registration, the one-time SharePoint Embedded guest registration, hosting, and wiring it into an MCP client. SECURITY.md documents the model and the residual risks to close before production. It's community code, not a certified product — review it and run a dependency scan before you point it at real data. But if you've been wanting to let an assistant read your Loop content without handing it the keys to the whole tenant, this pattern works. If you build on it or find a sharper approach, I'd love to hear it.