How do I get the native texture pointer to a camera's depth texture?

I need to use the depth texture in a native plugin. Although I can make a camera generate a depth texture, the only way I have found to access this is using a Unity-side shader with:

 sampler2D _CameraDepthTexture;

But my shaders are in the native plugin. How can I get a texture that I can send either as a texture or SRV pointer to C++?

The plugin is intended to be DX11-only in the first instance but a more general answer would be good.