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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def authenticate(self, request):
 """ Returns a two-tuple of `User` and token if a valid signature has been supplied using JWT-based authentication. Otherwise returns `None`. """

        jwt_value = self.get_jwt_value(request)
        if jwt_value is None:
            return None

        try:
            payload = jwt_decode_handler(jwt_value)
        except jwt.ExpiredSignature:
            msg = _('Signature has expired.')
            raise exceptions.AuthenticationFailed(msg)
        except jwt.DecodeError:
            msg = _('Error decoding signature.')
            raise exceptions.AuthenticationFailed(msg)
        except jwt.InvalidTokenError:
            raise exceptions.AuthenticationFailed()

        user = self.authenticate_credentials(payload)

        return (user, jwt_value)