@integrity-labs/xero-mcp-server

Augmented Team fork of @xeroapi/xero-mcp-server (MIT, Xero Limited) — same MCP server, plus XERO_TENANT_ID env-var support so multi-tenant OAuth tokens can be pinned to an explicit tenant.

Why this fork exists (ENG-4898)

The upstream MCP server is designed for Xero Custom Connections — a flow that issues single-tenant tokens via client_credentials. With those tokens the upstream's "always pick tenants[0]" behaviour is correct, because there's only ever one tenant in the list.

Augmented Team's integration uses 3-leg OAuth, which returns a multi-tenant access token: it grants access to every Xero organisation the OAuth user has previously connected. Without explicit tenant pinning, the upstream server picks whichever tenant Xero happens to return first — which is not necessarily the one the operator selected during consent. That's a cross-tenant data leak: an agent in Org A could return Org B's invoices.

This fork adds the missing knob:

 if (this.tenants && this.tenants.length > 0) {
-  this.tenantId = this.tenants[0].tenantId;
+  const desired = process.env.XERO_TENANT_ID;
+  if (desired) {
+    const match = this.tenants.find((t) => t.tenantId === desired);
+    if (!match) {
+      throw new Error(`XERO_TENANT_ID=${desired} not in token's tenant list…`);
+    }
+    this.tenantId = desired;
+  } else {
+    this.tenantId = this.tenants[0].tenantId;
+  }
 }

Set XERO_TENANT_ID in the MCP server's env to pin. Leave it unset and the behaviour matches upstream.

Failure mode if mis-configured

If XERO_TENANT_ID is set to an ID that the bearer token doesn't have access to, the server throws on updateTenants / requestToken with the available IDs in the error message. That's deliberate — silently falling back to tenants[0] is the original bug.

Upstream sync

When pulling a new upstream release:

1. git remote add xero-upstream https://github.com/XeroAPI/xero-mcp-server.git (one-time).
2. git fetch xero-upstream.
3. git merge --no-commit xero-upstream/main (or git checkout xero-upstream/main -- src/).
4. Re-apply the XERO_TENANT_ID env-var patch in src/clients/xero-client.ts (two call sites: MCPXeroClient.updateTenants and CustomConnectionsXeroClient.requestToken).
5. Bump version in package.json.
6. npm publish (public, @integrity-labs scope).

A tracking PR upstream would let us drop the fork once merged. See [Issue / PR link in ENG-4898].

License

MIT — same as upstream. See UPSTREAM_LICENSE for the original Xero notice.