As a consultant, I used to work at different clients premises.

It happens frequently that most of them has specific proxy settings, but not all the application I have installed on my laptop get settings from system preferences, for allowing me to change settings in one place.

Some of them bypass system preferences completely, proposing their own mask for entering specific data such as username, host and password.

I am looking for a convenient and not much intrusive way to share a common access point on which I could enter data, and maybe persist them.

An 'automatic' switching would be ideal, for example based on some network identification, but there's no problem for me to enter data manually.

I am not an IT expert, but to explain myself clearly, I am looking for a solution like .pac file is for browsers.

Relevant OS I am using are MacOSX and Linux (Ubuntu).