Author(s): Rizwanhoda

Originally published on Towards AI.

Your MCP server is about to give Claude access to your company’s most sensitive data. Here’s how to make sure only the right people get that access.

It was a Tuesday afternoon when the security team asked the question everyone dreads.

The article explains why authentication for MCP is essential—without it, anyone with access to Claude Desktop (or a stolen/left-behind device) can use configured MCP servers to retrieve sensitive data with no per-request login, authorization, or auditability. It then breaks down three MCP-compatible OAuth flows—Authorization Code for standard user login via existing providers, Client Credentials for service-to-service or automated agent access, and Device Code for systems that can’t use a browser—along with guidance on when to use each. Next, it walks through implementing OAuth for an MCP server using the Authorization Code flow, showing how to generate authorization URLs, exchange codes for tokens, validate tokens, and enforce authorization and auditing in tool calls, while also covering common mistakes (like insecure token storage, failing to validate tokens each request, missing expiration, forgetting audit logs, and not using HTTPS). Finally, it compares OAuth to API keys and JWT, outlines the real-world security impact of doing it correctly (instant access revocation and traceable actions), and provides next steps such as starting with Authorization Code, validating tokens every time, adding audit logging, setting short token lifetimes, and testing revocation.

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Published via Towards AI