Implementing an MCP Client with Browser-based OAuth

Overview

The purpose of this project is to implement an MCP Client with end-to-end OAuth support with a Streamable HTTP Server and then use it to inspect the transport and messages exchanged with the MCP Server.

Demo

https://github.com/user-attachments/assets/278bf15e-a762-47ac-8b2d-8f4a8e64eada

Operating Modes

At a minimum, this requires implementing an OAuthClientProvider that saves and retrieves auth information in session storage. When the user requests to connect with a server in the Connect panel, the client handles this through the useConnection hook, where the connect method works in two steps:

Step 1: No access token available -> (1) trigger OAuth flow through the server's authorize endpoint, (2) acquire an access token when the server returns an auth code

Step 2: Access token available, no transport set up: (1) create client and transport, (2) connect to server, (3) retrieve server capabilities

Step 1 precedes Step 2 to communicate with MCP Servers that require authorization. As such, this client will only work with servers that implement client authorization, specifically the /authorize and /token endpoints.

Once the client has connected to the server and server capabilities are available, the client offers users the option to list its tools in the Tools tab. Listing the prompts and resources available with the server has not been implemented yet (these tabs provide no content).

Once the list of tools are available, the user can choose to call any of the tools by entering the required input parameters in the Run panel.

As the tool is executed (through the server), the user can inspect the responses in the Inspect panel.

PS: If this seems similar to the MCP Inspector, it's not a coincidence. This project borrows a lot from it while maintaining as much simplicity as possible.