How to set a fieldmask on a grpc request?

[mctrafik]

This is probably more of a question than an issue, but I can't find anything in the docs.

I see that the FieldMasks are supported in a sense that field_mask is a common proto type and is imported from google/protobuf/field_mask.proto but how do I set it on an outgoing request?

[mctrafik]

Or does it have to be explicitly added to the request signature?