This issue came up in our game the other night. I made an on-the-spot adjudication, but I want to look into it further.

I've always worked on the assumption that by RAW light does not cast shadows.

The spell description notes that:

Completely covering the object with something opaque blocks the light.

The description does not address what partially covering the object does. On the assumption that a spell only does what it says it does, then a reasonable conclusion might be that partially blocking the light does not do anything. In other words, no shadows.

A counter-argument might be that it is only common sense that light from the cantrip casts shadows, because that's what light does, it casts shadows, and that it does not need to be spelled out in the definition, because it's the normal everyday interpretation of light.

A counter-counter argument would be, it's magic, it ain't physics.

So, my question is, does the light cantrip cast shadows?

Of course, the DM can interpret and/or make a house-rule. I'm interested in a RAW answer, and additionally, I'd be interested in what interpretation has worked for you.

The light spell casts shadows to the same degree that any light source does.

Technically speaking, nothing in the game rules ever says shadows exist whatsoever. The rules for light producing items just say they throw a radius of light, and that light level exists everywhere in the radius. Nothing in the rules says that physical objects like dense foliage block light in any way; nothing says that objects that create total cover have a shadow; there isn't even a rule in the book that says that walls block light!

Because there doesn't need to be. This is clearly one of those areas where the players and DM are just expected to understand how light works in the real world, and apply that understanding to the game. We're meant to just understand that light, whether from a torch or a spell, doesn't go through walls to illuminate the corridor beyond, because that's not what light does.

So while nothing says the light spell throws shadows, nothing says a torch does either. This should not be taken to mean that light sources in the game are different from real life light sources in terms of their behavior.

Yes, it casts shadows

You won't get a RAW answer much better than the wording of the spell you have already noted.

However I will point out that the wording for the light spell contains the identical text for the entry for torches:

providing bright light in a 20-foot radius and dim light for an additional 20 feet.

So it's reasonable to assume that is behaves in a similar manner to a torch.

You could consider looking at the Cover rules for what is means to obscure an object or provide cover from it. They say:

A target has total cover if it is completely concealed by an obstacle.

Therefore, any opaque object that can conceal the object affect by light provides total cover.

You can then look at the general spellcasting rules for Area of Effect. Technically, light doesn't have an area of effect, being a targeted spell with the effect to emit light. However this is the only rules on area of effect we have to go on.

A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total cover.

If you combine all the rules quoted with the rule you gave, it is safe to assume that RAI are that light casts shadows.