An authentication-delegating service implemented in an authentication server or other processing device is configured to receive a request from a relying party for delegated authentication information associated with a particular user, to determine a level of trust associated with the relying party, and to provide the delegated authentication information to the relying party if the relying party has a sufficient level of trust, so as to permit the relying party to authenticate the user based on the delegated authentication information. The delegated authentication information has the property that the user can be presently authenticated based on such information. The delegated authentication information may comprise, for example, at least one value derived from a one-time password or other authentication credential of the particular user. The authentication-delegating service may be graded to provide different types of delegated authentication information based on respective levels of trust that may be associated with relying parties.