# client-id-metadata-document

Source: https://startwithidentity.com/glossary/client-id-metadata-document/
Last updated: 2026-10-30
License: content by Start with Identity. Cite the source URL.

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An OAuth Client ID Metadata Document (CIMD) is a JSON document of client metadata hosted at an HTTPS URL that the client uses as its `client_id`, so an authorization server can fetch and verify the client's details on first contact without any prior registration. It is specified in [draft-ietf-oauth-client-id-metadata-document](https://datatracker.ietf.org/doc/draft-ietf-oauth-client-id-metadata-document/), an active IETF OAuth Working Group draft that is not yet an RFC as of October 2026.

CIMD solves the open-ecosystem problem: thousands of AI clients connecting to thousands of servers that have never met. Dynamic Client Registration (RFC 7591) handles that by letting anyone create a client, which fills authorization servers with unverifiable, unbounded registrations. With CIMD the client's identity is a URL the server can check, cache, and allow or block by domain, and the redirect URIs come from a document the client's owner controls. The Model Context Protocol authorization spec tells clients to prefer CIMD over Dynamic Client Registration when the server advertises `client_id_metadata_document_supported`. Servers fetching the URL need SSRF protection (the draft has a section on it), and a valid document proves control of a domain, not that the client is trustworthy, so consent screens still need to show that domain clearly.

See also: [dynamic client registration](https://startwithidentity.com/glossary/dynamic-client-registration/), [MCP authorization](https://startwithidentity.com/glossary/mcp-authorization/), [authorization server metadata](https://startwithidentity.com/glossary/authorization-server-metadata/), [authorization server](https://startwithidentity.com/glossary/authorization-server/), [Aaron Parecki](https://startwithidentity.com/experts/aaron-parecki/), [agent identity standards map 2026](https://startwithidentity.com/reports/agent-identity-standards-map-2026/)