'Validates access to the request realm.
How providers choose to use the realm parameter is outside the OAuth
specification but it is commonly used to restrict access to a subset
of protected resources such as "photos".
required_realm is a convenience parameter which can be used to provide
a per view method pre-defined list of allowed realms.'

def validate_realm(self, client_key, access_token, uri=None, required_realm=None):

    raise NotImplementedError('Subclasses    must    implement    this    function.')
