def header_property(wsgi_name):
    """Create a read-only header property.

    Args:
        wsgi_name (str): Case-sensitive name of the header as it would
            appear in the WSGI environ ``dict`` (i.e., 'HTTP_*')

    Returns:
        A property instance than can be assigned to a class variable.

    """

    def fget(self):
        try:
            return self.env[wsgi_name] or None
        except KeyError:
            return None

    return property(fget)