I have to input the username and password everytime I use the samba service.
If I close the pantheon-files at the samba directory, the next time I open it, it will ask for my password twice, it is so annoying.
If you are comfortable using the command line, the advice here will help you:
Basically, you need to create an entry in /etc/fstab that will try to mount your drive with password provided automatically.
Perhaps there is a way the GUI could be improved, but in the short term this should solve your problem (if you are regularly away from the share's network, it will cause a failed mount, but I think that is OK so long as you don't make any system stuff dependent)