auth-source-protocols

auth-source-protocols is a variable defined in `auth-source.el'.
Its value is

((imap "imap" "imaps" "143" "993")
 (pop3 "pop3" "pop" "pop3s" "110" "995")
 (ssh "ssh" "22")
 (sftp "sftp" "115")
 (smtp "smtp" "25"))

Documentation:
List of authentication protocols and their names

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.2 of Emacs.