Calendar MCP Server with SSO and Tool-Level Scopes

This example demonstrates how to build a secure calendar MCP server that:

• Restricts access to only registered MCP clients (Claude Desktop and ChatGPT)
• Requires SSO authentication via Okta or Azure AD for "Tenant A"
• Grants write access only to users with the scheduler permission in "Tenant A"
• Allows read-only access to all other authenticated users

Step 1: Configure the MCP Server

1. Create an MCP Server in Descope:

   • Navigate to MCP Servers and create a new MCP Server
   • Enable Dynamic Client Registration (DCR) to allow Claude and ChatGPT clients to register automatically
   • Create a Client Registration Flow, configure Approved Redirect URLs to restrict registration:

     claude://oauth-callback/*
     https://chat.openai.com/oauth/callback/*

   This ensures only Claude Desktop and ChatGPT can register as OAuth clients.

2. Define MCP Tool Scopes:

   • mcp:calendar.write - Permission to create, update, or delete calendar events
   • mcp:calendar.readonly - Permission to read calendar events and query availability

3. Configure the Consent Flow:

   • Create a Descope Flow that handles user consent
   • Set this as the Flow Hosting URL in your Inbound App settings
   • The flow will display which scopes the MCP client is requesting

Step 2: Set Up SSO for Tenant A

1. Configure SSO Providers:

   • For Tenant A: Set up Okta or Azure AD as the SSO provider

2. Map SSO Groups to Descope Permissions:

   • In your SSO provider (Okta or Azure AD), create a group called "Schedulers"
   • Configure Descope to map this group to a scheduler permission
   • Users in the "Schedulers" group will automatically receive the scheduler permission in their JWT claims

Step 3: Create Access Control Policies

Create a policy that enforces the following rules:

Policy: Scheduler Write Access

• Conditions:
  • user.tenantIds contains tenant-a
  • user.permissions contains scheduler
• Allowed Scopes: mcp:calendar.write, mcp:calendar.readonly

Policy: Read-Only Access for All Others

• Conditions:
  • N/A
• Allowed Scopes: mcp:calendar.readonly only

User Flow

Once you've configured everything, here's what will happen when a user connects their MCP client to your MCP server:

1. Client Registration:

   • Claude Desktop or ChatGPT will self-register with Descope either via CIMD or via DCR (depending on the client implementation)
   • Descope validates the redirect URI against approved patterns

2. User Authentication:

   • The MCP client redirects the user to Descope's authorization endpoint
   • Descope detects the user's tenant (A or B), based on the user's email address, and redirects to the appropriate SSO provider
   • User authenticates via their SSO provider
   • SSO provider returns user and group attributes, that are mapped accordingly based on your tenant configuration to Descope roles
   • In the consent flow, the user should also connect to Google using Connections so that Descope can store the necessary Google OAuth token for future MCP tool usage

3. Consent and Token Issuance:

   • User is presented with a consent screen showing requested scopes
   • User grants consent to use the MCP server
   • Descope evaluates access control policies:
     • If user has scheduler permission in Tenant A or B → token includes mcp:calendar.write and mcp:calendar.readonly
     • Otherwise → token includes only mcp:calendar.readonly
   • Access token is issued with appropriate scopes

4. Tool Execution:

   • MCP client makes a request to execute create_calendar_event tool, sending the Descope access token
   • MCP server validates the access token, checks the aud claim, and verifies the mcp:calendar.write scope
   • If scope is missing → MCP server returns 403 Forbidden - Insufficient Scope
   • If scope is present → MCP server exchanges the Descope access token with the Google Calendar Connection to retrieve the Google access token with calendar write permissions
   • MCP server uses the Google access token to make an API request to Google Calendar API to schedule the meeting
   • Google Calendar API returns the created event details
   • MCP server returns the result to the MCP client

Complete Flow Diagram

Here is a mermaid diagram of how this is supposed to work, from start to finish: