'Returns the H(A2) string. See :rfc:`2617` section 3.2.2.3.'

def H_A2(self, data):

    if (self.qop == u'auth-int'):
        a2 = (u'%s:%s:%s' % (data.method, self.uri, self.H(data.peek())))
    else:
        a2 = (u'%s:%s' % (data.method, self.uri))
    return self.H(a2)
