Check signature of signed request.

def check_signature(self):
        """Check signature of signed request."""
        if not self.signature:
            return True
        signature_value = request.headers.get(self.signature, None)
        if signature_value:
            validator = 'check_' + re.sub(r'[-]', '_', self.signature).lower()
            check_signature = getattr(signatures, validator)
            if check_signature(signature_value, request.data):
                return True
        return False