According to Kepler"s second law of planetary motion, the radius vector joining planet to the

sun sweeps out equal areas, in equal interval of time.
i.e., constant

According to figure, r be the position vector of the planes w.r.t. sun and F be the gravitational force. on the planet due to the sun. Then, torque exerted on the planet by this force about the sun is

Angular momentum constant
Hence, kepler's second law (law of areas) is equivalent to low of conservation of angular momentum.