A foaf:openid is a property of a foaf:Agent that associates it with a document that can be used as an indirect identifier in the manner of the OpenID "Identity URL". As the OpenID 1.1 specification notes, OpenID itself"does not provide any mechanism to exchange profile information, though Consumers of an Identity can learn more about an End User from any public, semantically interesting documents linked thereunder (FOAF, RSS, Atom, vCARD, etc.)". In this way, FOAF and OpenID complement each other; neither provides a stand-alone approach to online "trust", but combined they can address interesting parts of this larger problem space.

The foaf:openid property is "inverse functional", meaning that anything that is the foaf:openid of something, is the foaf:openid of no more than one thing. FOAF is agnostic as to whether there are (according to the relevant OpenID specifications) OpenID URIs that are equally associated with multiple Agents. FOAF offers sub-classes of Agent, ie. foaf:Organization and foaf:Group, that allow for such scenarios to be consistent with the notion that any foaf:openid is the foaf:openid of just one foaf:Agent.

FOAF does not mandate any particular URI scheme for use as foaf:openid values. The OpenID 1.1 specification includes a delegation model that is often used to allow a weblog or homepage document to also serve in OpenID authentication via "link rel" HTML markup. This deployment model provides a convenient connection to FOAF, since a similar technique is used for FOAF autodiscovery in HTML. A single document can, for example, serve both as a homepage and an OpenID identity URL.