MCP Auth Gets Real: What the 2026-07-28 Spec Means for Local MCP Servers Behind a Tunnel
Authentication is the part of MCP that tends to get postponed. A May 2026 measurement study put it plainly: many remote servers treat it as a deployment add-on rather than a security boundary. The 2026-07-28 revision of the Model Context Protocol specification tightens the rules for any server that does use authorization. It keeps OAuth 2.1 resource-server behavior, pins down how a client…
The 2026-07-28 revision of the Model Context Protocol (MCP) specification introduces several significant changes to authentication and authorization. The revision tightens the rules for servers using authorization, keeps OAuth 2.1 resource-server behavior, formally deprecates Dynamic Client Registration (DCR), and makes Client ID Metadata Documents (CIMD) the recommended way for an app to identify itself.
This matters even for local MCP servers behind a tunnel, as the public tunnel URL becomes the token audience, which every access token is bound to. The guide covers what changed, what a tunnel must preserve, and how to verify the chain with curl.
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