dsh-oauth-mcp-client: OAuth 2.1 MCP Client Plugin for DeepSeek Harness

`dsh-oauth-mcp-client` is an MIT-licensed client plugin designed for DeepSeek Harness (DSH). It aims to address challenges such as OAuth 2.1 authorization, dynamic client registration, browser callbacks, and token storage when accessing external MCP services that require authentication. The plugin comes with built-in configurations for connecting to the Springbrand production MCP Gateway (`https://connector.springbrand.ai/mcp`), supporting the OAuth 2.1 PKCE flow, automatic reconnection, and the discovery, registration, and execution of MCP tools. Its core code is adapted from `@deepseek-ai/dsh-mcp-client`, with OAuth state managed through DS...