Support clock drift in Omniauth SAML provider (#15511)

The setting is not well documented by the provider, but allows for
clock skew between SP and IDP, see:
https://github.com/omniauth/omniauth-saml/blob/master/spec/omniauth/strategies/saml_spec.rb

Co-authored-by: kaiyou <dev@kaiyou.fr>

config/initializers/omniauth.rb

@@ -60,6 +60,7 @@ Devise.setup do |config|
     saml_options[:attribute_statements][:verified] = [ENV['SAML_ATTRIBUTES_STATEMENTS_VERIFIED']] if ENV['SAML_ATTRIBUTES_STATEMENTS_VERIFIED']
     saml_options[:attribute_statements][:verified_email] = [ENV['SAML_ATTRIBUTES_STATEMENTS_VERIFIED_EMAIL']] if ENV['SAML_ATTRIBUTES_STATEMENTS_VERIFIED_EMAIL']
     saml_options[:uid_attribute] = ENV['SAML_UID_ATTRIBUTE'] if ENV['SAML_UID_ATTRIBUTE']
+    saml_options[:allowed_clock_drift] = ENV['SAML_ALLOWED_CLOCK_DRIFT'] if ENV['SAML_ALLOWED_CLOCK_DRIFT']
     config.omniauth :saml, saml_options
   end
 end