admin: add support for displaying san in certs end point (#4566)

*Description*: Adds support for displaying Subject Alternate Names as a comma separated list of string in `/certs` admin end point

*Risk Level*: Low
*Testing*: Automated
*Docs Changes*: Updated
*Release Notes*: Updated

Signed-off-by: Rama <rama.rao@salesforce.com>

Mirrored from https://github.com/envoyproxy/envoy @ 7403314b0b255a89ab284b7ed0eead5a5f4aecfd

docs/BUILD

@@ -12,6 +12,7 @@ package_group(
 proto_library(
     name = "protos",
     deps = [
+        "//envoy/admin/v2alpha:certs",
         "//envoy/admin/v2alpha:clusters",
         "//envoy/admin/v2alpha:config_dump",
         "//envoy/admin/v2alpha:memory",

envoy/admin/v2alpha/BUILD

@@ -37,3 +37,9 @@ api_proto_library_internal(
     srcs = ["memory.proto"],
     visibility = ["//visibility:public"],
 )
+
+api_proto_library_internal(
+    name = "certs",
+    srcs = ["certs.proto"],
+    visibility = ["//visibility:public"],
+)

envoy/admin/v2alpha/certs.proto

@@ -0,0 +1,45 @@
+syntax = "proto3";
+
+package envoy.admin.v2alpha;
+
+// [#protodoc-title: Certificates]
+
+// Proto representation of certificate details. Admin endpoint uses this wrapper for `/certs` to
+// display certificate information. See :ref:`/certs <operations_admin_interface_certs>` for more
+// information.
+message Certificates {
+  // List of certificates known to an Envoy.
+  repeated Certificate certificates = 1;
+}
+
+message Certificate {
+
+  // Details of CA certificate.
+  repeated CertificateDetails ca_cert = 1;
+
+  // Details of Certificate Chain
+  repeated CertificateDetails cert_chain = 2;
+}
+
+message CertificateDetails {
+  // Path of the certificate.
+  string path = 1;
+
+  // Certificate Serial Number.
+  string serial_number = 2;
+
+  // List of Subject Alternate names.
+  repeated SubjectAlternateName subject_alt_names = 3;
+
+  // Minimum of days until expiration of certificate and it's chain.
+  uint64 days_until_expiration = 4;
+}
+
+message SubjectAlternateName {
+
+  // Subject Alternate Name.
+  oneof name {
+    string dns = 1;
+    string uri = 2;
+  }
+}