feat(unseal): add unseal protocol support for user agents

protobufs/client.proto

@@ -0,0 +1,17 @@
+syntax = "proto3";
+
+package arbiter;
+
+import "auth.proto";
+
+message ClientRequest {
+  oneof payload {
+    arbiter.auth.ClientMessage auth_message = 1;
+  }
+}
+
+message ClientResponse {
+  oneof payload {
+    arbiter.auth.ServerMessage auth_message = 1;
+  }
+}