Automatically purging binlogs after successful replication
Server is responsible to purge their own file. Guess what happens if your master has two slaves and one of it catches up faster deleting logs required for second?!!

So yes expire_logs_days is the way to go. Set that value wisely and let master do its business. 

That said why do you want to purge logs? You have purge binary logs to command but I'd still let purging upto master unless disk is critical.

If you want it, then you can script out the manual purging logic:
Check all slaves have caught up to latest 
Purge a logs before the exec_master_log_file.

In my opinion this is absolutely unnecessary unless there some odd requirement that u just can't think about...