@Suspendable abstract fun externalIdForPublicKey(publicKey: PublicKey): UUID?
This method allows lookups of PublicKeys to an associated "external ID" / UUID. Providing a PublicKey that is unknown by the node or is not mapped to an external ID will return null. Otherwise, if the PublicKey has been mapped to an external ID, then the UUID for that external ID will be returned. The method looks up keys generated by the node as well as keys generated on other nodes and registered with the IdentityService.
publicKey - the PublicKey used to perform the lookup to external ID