code: func authz2ModelMapToPB(m map[string]authz2Model) (*sapb.Authorizations, error) {
  	resp := &sapb.Authorizations{}
  	for k, v := range m {
  		// Make a copy of k because it will be reassigned with each loop.
  		kCopy := k
  		authzPB, err := modelToAuthzPB(&v)
  		if err != nil {
  			return nil, err
  		}
  		resp.Authz = append(resp.Authz, &sapb.Authorizations_MapElement{Domain: &kCopy, Authz: authzPB})
  	}
  	return resp, nil
  }
docs: // authz2ModelMapToPB converts a mapping of domain name to authz2Models into a
  // protobuf authorizations map