Address feedback - Round container-storage-interface#3

Author: saad-ali

spec.md

@@ -444,6 +444,9 @@ message CreateVolumeRequest {
 
   // End user credentials used to authenticate/authorize volume creation
   // request.
+  // These Credentials are not passed in on DeleteVolume calls. If an SP
+  // requires these credentials on DeleteVolume calls, it SHOULD cache the
+  // credentials for use on subsequent DeleteVolume calls.
   // This field is OPTIONAL.
   Credentials user_credentials = 6;
 }
@@ -650,6 +653,10 @@ message ControllerPublishVolumeRequest {
 
   // End user credentials used to authenticate/authorize controller publish
   // request.
+  // These Credentials are not passed in on ControllerUnpublishVolume calls. If
+  // an SP requires these credentials on ControllerUnpublishVolume calls, it
+  // SHOULD cache the credentials for use on subsequent
+  // ControllerUnpublishVolume calls.
   // This field is OPTIONAL.
   Credentials user_credentials = 6;
 }
@@ -947,6 +954,9 @@ message NodePublishVolumeRequest {
   bool readonly = 7;
 
   // End user credentials used to authenticate/authorize node publish request.
+  // These Credentials are not passed in on NodeUnpublishVolume calls. If an SP
+  // requires these credentials on NodeUnpublishVolume calls, it SHOULD cache
+  // the credentials for use on subsequent NodeUnpublishVolume calls.
   // This field is OPTIONAL.
   Credentials user_credentials = 8;
 }