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

A developer built an open-source MCP server called loop-reader-mcp to give AI assistants read-only access to Microsoft Loop pages without breaking permissions. The solution splits discovery and retrieval across two identities: user-level OBO tokens for search and app-only identity for content retrieval, gated by a per-user cache to prevent permission flattening.

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 . 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. 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 insight that cracked it: Graph Search is security-trimmed for delegated callers, even for SPE content. Search respects the user's permissions; only 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. php 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 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. 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. driveId, itemId pairs, not just the item IDThe code is on GitHub under MIT: github.com/DenizV/loop-reader-mcp . The README covers the SECURITY.md documents the model andIt'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.