Slope Limit on Rigidbody First Person Controller

I need to use the Rigidbody First Person Controller for my game, but I've noticed that it doesn't actually have a slope limit -My character can just walk up mountains like it's nobody's business.

The Rigidbody First Person Controller does have a slope curve modifier, but tweaking around with it hasn't solved my problem.

So...

How would I modify the Rigidbody First Person Controller script to make it so that the player will slide down steep slopes and prevent the player from jumping while facing one?

I'm sure I need to use raycasting to achieve this, but I'm not sure how I would.

Thanks for your help!