How to Build an Auth-Ready MCP Server With Next.js and Descope

Authentication is presented as the main challenge in building Model Context Protocol servers because OAuth-based clients require secure token issuance, discovery endpoints, claim-based permissions, and request verification, all of which can otherwise require operating a separate OAuth/OIDC system. The walkthrough uses a Next.js App Router server with mcp-handler, jose for local JWT verification, zod for input validation, Descope as an inbound OAuth/OIDC provider, mcp-remote for local Claude Desktop testing, and Vercel deployment. Descope supplies authorization endpoints, OIDC discovery, JWKS keys, configurable MCP scopes, policies, and client registration, while the MCP server verifies bearer tokens, validates issuer and audience, extracts scopes, roles, and identity claims, and enforces permissions inside individual tool handlers. Recommended authorization patterns include checks for OAuth scopes, user roles, email domains, or combinations of these controls. An AuthTown Slack integration illustrates how person-specific JWTs support both access control and accountability when searching public or private community channels, unlike shared API keys that cannot identify the requester. The guide also advises using the current registerTool SDK method, clearing cached local tokens when testing changed permissions, caching OIDC discovery and JWKS configuration, logging received claims during development, and ensuring production token audiences and server URLs match deployment settings.

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