Use the devise config rather than the constant

app/models/service.rb

@@ -1,9 +1,7 @@
 class Service < ApplicationRecord
   belongs_to :user
 
-  PROVIDERS = %w{ facebook twitter github }
-
-  PROVIDERS.each do |provider|
+  Devise.omniauth_configs.keys.each do |provider|
     scope provider, ->{ where(provider: provider) }
   end
 
@@ -31,4 +29,4 @@ class Service < ApplicationRecord
   end
 
   def twitter_refresh_token!(token); end
-end
+end

template.rb

@@ -185,7 +185,7 @@ def add_multiple_authentication
 
     template = """
     env_creds = Rails.application.credentials[Rails.env.to_sym] || {}
-    Service::PROVIDERS.each do |provider|
+    %w{ facebook twitter github }.each do |provider|
       if options = env_creds[provider]
         confg.omniauth provider, options[:app_id], options[:app_secret], options.fetch(:options, {})
       end