Saving session tokens by default? (or: other ways to save login info)

I have stored my credentials in my `.authinfo.gpg` file, it would be nice to be able to have ement use those credentials. For example, this call will lookup the password:

(auth-source-pick-first-password :host "element.io")

or to be more specific in the event of multiple "element.io" passwords:

(auth-source-pick-first-password :host "element.io" :user "@me:matrix.org")

In theory, the user would type in their username on connect, then if one of the above incantations didn't return a password, prompt the user for their password and maybe offer to store it in their `.authinfo.gpg` file, if `gnupg` is installed. (maybe checking with:

(executable-find "gpg")

and then not offering to store the password if that command returns `nil`).