Frontchannel_logout_uri is an OpenID Connect OPTIONAL Relying Party URL that will cause the Relying Party to log itself out when rendered in an iframe by the OpenID Connect Provider.

An iss (issuer) URI Query parameter and a sid (session ID) URI Query parameter MAY be included by the OpenID Connect Provider to enable the Relying Party to validate the request and to determine which of the potentially multiple sessions is to be logged out; if either URI Query parameter is included, both MUST be.

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