<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_token(self, token, scopes_required=None):
 """ This function can be used to validate tokens. Note that this only works if a token introspection url is configured, as that URL will be queried for the validity and scopes of a token. :param scopes_required: List of scopes that are required to be granted by the token before returning True. :type scopes_required: list :returns: True if the token was valid and contained the required scopes. An ErrStr (subclass of string for which bool() is False) if an error occured. :rtype: Boolean or String .. versionadded:: 1.1 """

        valid = self._validate_token(token, scopes_required)
        if valid is True:
            return True
        else:
            return ErrStr(valid)