How can I run a package setup only once?

Question

I'm writing a package to interact with a web service via HTTP API. But I need to make an action once to get permission to send my data. This action must be made just one time.
How can I configure my package to run this setup function only once after installed?

Answer 1

Well you need to save this information somewhere persistently.

You might write data to a package-specific config file (see locate-user-emacs-file), but the simplest approach is probably to use defcustom to define an option indicating whether or not the setup has been completed, and to call (customize-save-variable 'VARNAME VALUE) in your code once setup is complete.

I'm assuming that the setup isn't already creating variable values that you could test for.