Return a tuple containing client authentication data.

def GetAuth(self):
        '''Return a tuple containing client authentication data.
        '''
        if self.auth: return self.auth
        for elt in self.ps.GetMyHeaderElements():
            if elt.localName == 'BasicAuth' \
            and elt.namespaceURI == ZSI_SCHEMA_URI:
                d = _auth_tc.parse(elt, self.ps)
                self.auth = (AUTH.zsibasic, d['Name'], d['Password'])
                return self.auth
        ba = self.environ.get('HTTP_AUTHENTICATION')
        if ba:
            ba = ba.split(' ')
            if len(ba) == 2 and ba[0].lower() == 'basic':
                ba = _b64_decode(ba[1])
                self.auth = (AUTH.httpbasic,) + tuple(ba.split(':'))
                return self.auth
        self.auth = (AUTH.none,)
        return self.auth