[1] RFC 6125 - Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS) ( 版) <https://tools.ietf.org/html/rfc6125#section-1.8>
application service type: A formal identifier for the application
protocol used to provide a particular kind of application service
at a domain; the application service type typically takes the form
of a Uniform Resource Identifier scheme [URI] or a DNS SRV Service
[DNS-SRV].