Character Controller velocity match separate forward/backwards and left/right move speeds

I'm using Unity's character controller for moving my player, and I'm adding the vertical input to a Speed variable for forwards/backwards movement and adding the horizontal input to a Strafe variable for the left/right movement. These are then put into a vector3 that goes to charactercontroller.Move() to make the player move.

I need to make sure that when CharacterController performs it's colision detection, my Speed and Strafe variables match the read-only CharacterController.velocity value.

If I get the magnitude of CharacterController.velocity, it *almost* matches my Speed variable (to 4 decimal points) which is close enough, but this only works if I'm using vertical input, otherwise my Strafe speed is factored in and now the magnitude of CharacterController.velocity returns Speed + Strafe.

Further more, the magnitude of CharacterController.velocity is absolute, so I need to work out if the player is moving backwards or forwards, or left or right.

I'm not entirely sure how I should be comparing my two movement speed variables to the single CharacterController.velocity vector and somehow matching my two speed variables to it?

 

So, combining the charactercontroller.velocity.x and charactercontroller.velocity.z magnitude according to https://docs.unity3d.com/ScriptReference/CharacterController-velocity.html allows you to get the forwards speed, I'm not 100% certain if this is including my strafing speed, but I can't figure out at all how to separate the forward speed from the side-to-side speed to match my variables to character controller's internal velocity speeds?