Securing MCP Servers: Role-Based Tool Access with OAuth 2.0 and Auth0

Welcome back to the channel! In today's video, we're diving deep into securing your MCP (Model Context Protocol) server using O-Zero with role-based authentication and authorization. This is the third installment in my MCP security series – I've previously covered Microsoft Entra ID and AWS Cognito, and now we're tackling O-Zero to give you a complete understanding of different authentication providers.

Why This Matters:
As MCP servers become more critical in AI-powered applications, securing them properly is essential. Whether you're building internal tools or customer-facing applications, you need granular control over who can access specific tools within your MCP server. This tutorial gives you exactly that – a production-ready approach to role-based security that you can implement immediately.

What We'll Build:
We'll create an MCP server from scratch with four tools – two public tools that anyone can access, and two secure tools that require specific permissions. Using O-Zero as our identity provider, we'll configure authentication and authorization so that access tokens determine exactly which tools a client can see and use. The result is a flexible, token-driven security model that scales with your application needs.

📌 What You'll Learn:

1. MCP Server Development

Setting up an MCP server project in .NET

Creating public tools using [McpServerTool] attribute

Creating secure tools with [Authorize] attribute

Using WithToolsFromAssembly() for automatic tool discovery

Understanding MCP server transports and configuration

2. O-Zero Configuration

Creating an API resource with custom identifier

Setting up user access vs. client access policies

Defining custom permissions for each secure tool

Configuring client applications for machine-to-machine communication

Enabling role-based access and token permissions

3. Authentication Implementation

Adding JWT Bearer authentication to your MCP server

Configuring authority and audience from app settings

Validating token issuer and audience

Handling authentication failure events

Understanding token validation lifecycle

4. Authorization & Policy Management

Creating custom authorization policies

Implementing permission validation logic

Extracting claims from authenticated user context

Parsing and validating scope/permission claims

Returning true/false based on token permissions

5. Testing & Validation

Generating access tokens using Postman

Inspecting token claims and permissions

Testing different permission combinations

Verifying public tools remain accessible without auth

Validating secure tools appear only with correct permissions

🛠️ Tech Stack & Tools Used:

MCP Server: .NET-based Model Context Protocol implementation

O-Zero: OAuth 2.0 / OpenID Connect identity provider

Authentication: JWT Bearer Authentication (Microsoft.AspNetCore.Authentication.JwtBearer)

Framework: ASP.NET Core

Testing: Postman for API requests and token generation

Packages: MCP Server NuGet package (v0.6.0-alpha1)

⏱️ Timestamps:

00:00 – Introduction & Problem Statement
01:15 – Quick Demo: Before & After Security Implementation
02:45 – Creating Public MCP Tools
04:30 – Adding Secure Tools with Authorize Attribute
06:20 – MCP Server Basic Configuration
08:10 – O-Zero Console: Creating Your API
10:45 – Setting Up API Permissions
12:30 – O-Zero Console: Application Configuration
14:15 – Client Access vs. User Access Explained
16:00 – Generating Your First Access Token (Postman)
18:30 – Inspecting Token Claims
20:15 – Implementing Authentication in Program.cs
23:00 – Adding Authorization Policies
25:45 – Writing Custom Permission Validator
28:30 – Extracting and Parsing Claims
31:15 – Testing with Both Permissions
33:45 – Testing with Partial Permissions
35:30 – Testing with No Permissions
37:15 – Complete Code Review
39:00 – Key Takeaways & Best Practices
40:30 – Outro & Support Request

🎯 Who Is This For?

.NET developers building MCP servers

Developers implementing authentication/authorization

Teams building AI-powered applications with MCP

Anyone interested in OAuth 2.0 and role-based security

DevOps engineers securing API endpoints

❓ Common Questions Answered:

How do I make some tools public and others secure?

What's the difference between user access and client access?

How do I extract permissions from an access token?

Can I have multiple policies for different tools?

How do I test my MCP server security?

What happens if a token has no permissions?

How do I configure O-Zero for machine-to-machine auth?

💬 Community & Support:
Have questions about this implementation? Drop them in the comments below! I read every comment and do my best to respond within 48 hours. If you're facing specific issues, please include error messages and code snippets so I can help you better.

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