tlsSocket.getCertificate()
返回表示本地证书的对象。返回的对象有一些与证书字段对应的属性。
¥Returns an object representing the local certificate. The returned object has some properties corresponding to the fields of the certificate.
有关证书结构的示例，请参见 tls.TLSSocket.getPeerCertificate()。
¥See tls.TLSSocket.getPeerCertificate() for an example of the certificate
structure.
如果没有本地证书，则将返回空对象。如果套接字被销毁，则返回 null。
¥If there is no local certificate, an empty object will be returned. If the
socket has been destroyed, null will be returned.