*: developer machine HSPKI credentials

In addition to k8s certificates, prodaccess now issues HSPKI
certificates, with DN=$username.sso.hswaw.net. These are installed into
XDG_CONFIG_HOME (or os equiv).

//go/pki will now automatically attempt to load these certificates. This
means you can now run any pki-dependant tool with -hspki_disable, and
with automatic mTLS!

Change-Id: I5b28e193e7c968d621bab0d42aabd6f0510fed6d
diff --git a/cluster/prodvider/proto/prodvider.proto b/cluster/prodvider/proto/prodvider.proto
index 1ae2798..ba5bf9d 100644
--- a/cluster/prodvider/proto/prodvider.proto
+++ b/cluster/prodvider/proto/prodvider.proto
@@ -15,6 +15,7 @@
     }
     Result result = 1;
     KubernetesKeys kubernetes_keys = 2;
+    HSPKIKeys hspki_keys = 3;
 }
 
 message KubernetesKeys {
@@ -24,6 +25,13 @@
     bytes key = 4;
 }
 
+message HSPKIKeys {
+    bytes ca = 1;
+    bytes cert = 2;
+    bytes key = 3;
+    string principal = 4;
+}
+
 service Prodvider {
     rpc Authenticate(AuthenticateRequest) returns (AuthenticateResponse);
 }