docs: def validate_api_headers(param, value):
      """Validate that API headers is a CSV of k=v pairs."""
      # pylint: disable=unused-argument
      if not value:
          return None
  
      headers = {}
      for kv in value.split(","):
          try:
              k, v = kv.split("=", 1)
              k = k.strip()
  
              for bad_header in BAD_API_HEADERS:
                  if bad_header == k:
                      raise click.BadParameter(
                          "%(key)s is not an allowed header" % {"key": bad_header},
                          param=param,
                      )
  
              if k in API_HEADER_TRANSFORMS:
                  transform_func = API_HEADER_TRANSFORMS[k]
                  v = transform_func(param, v)
          except ValueError:
              raise click.BadParameter(
                  "Values need to be a CSV of key=value pairs", param=param
              )
  
          headers[k] = v
  
      return headers