docs: def _split_header(header):
          """Turn Authorization: header into parameters."""
          params = {}
          parts = header.split(',')
          for param in parts:
              # Ignore realm parameter.
              if param.lower().startswith('realm='):
                  continue
              # Remove whitespace.
              param = param.strip()
              # Split key-value.
              param_parts = param.split('=', 1)
              # Remove quotes and unescape the value.
              params[param_parts[0]] = unquote(param_parts[1].strip('\"'))
          return params