The foreman-config script since #2343 doesn't change boolean settings:

2.0.0p0 :001 > Setting.find_by_name('signo_sso').value
  Setting Load (0.2ms)  SELECT "settings".* FROM "settings" WHERE "settings"."name" = 'signo_sso' ORDER BY name LIMIT 1
 => false 

$ script/foreman-config -e development -k signo_sso -v true
true

2.0.0p0 :002 > Setting.find_by_name('signo_sso').value
  Setting Load (0.2ms)  SELECT "settings".* FROM "settings" WHERE "settings"."name" = 'signo_sso' ORDER BY name LIMIT 1
 => false 

It appears this is due to the interface change on the setting model, where the controller was updated and not this script, which interacts directly with the model.

(from https://bugzilla.redhat.com/show_bug.cgi?id=976578)