A player comes into the penalty area with the ball and takes a shot - 
losing his shoe in the process. 

The goalkeeper makes the save but cannot control the ball. 

The goalkeeper dives for the loose ball but comes up only with the shoe. 

As another attacker takes a shot, the goalkeeper throws the shoe at the ball 
deflecting it across the goal line.  

Stop play, caution the goalkeeper for unsporting behavior for bringing the game into disrepute. The goalkeeper action is not a foul but it is a misconduct.

The shoe thrown by the keeper is an extension of his hand and he is the only one that he is allowed to handle the ball within his penalty area.

Restart with an indirect free kick in favor of the attacking team at the spot where the shoe made contact with the ball, subject to special circumstances in Law 8.

Within the meaning of the law this is not an obvious goal scoring opportunity.