In preparation for adding support for TPM attestations as an authentication
method in bx509d for a host trust bootstrap mechanism based on TPMs and their
endorsement keys and endorsement key certificates.
The plan is to add support to libhx509 and hxtool for PermanentIdentifier
(RFC4043) and HardwareModuleName (RFC4108) SANs, and then to add a query
parameter to bx509d for passing an attestation and a proof-of-possession
(either CMS or CSR), and add an authorizer plugin call for authorizing a device
manufacturer and serial number to hostname. Support for TPMs w/o endorsement
key certificates should also be possible based on a digest of the endorsement
key as the "serial number".
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