Wall climb effect on player (how to detect player block collision?)

I'm trying to give the player a permanent wall climbing effect similar so they basically treat any block as a ladder (similar to a spider), but can't find a way to detect when the player is colliding with a block. 

The closest I can get is detecting when a block is in front of the player, but I need to detect when the player is pressing up against the block. 

Is there some sort of way to detect when the player is moving into a block?