FEATURE: Add support for signle logout service

lib/saml_authenticator.rb

@@ -51,12 +51,14 @@ class SamlAuthenticator < ::Auth::OAuth2Authenticator
                       name: name,
                       issuer: Discourse.base_url,
                       idp_sso_target_url: setting(:target_url),
+                      idp_slo_target_url: setting(:slo_target_url),
                       idp_cert_fingerprint: GlobalSetting.try(:saml_cert_fingerprint),
                       idp_cert_fingerprint_algorithm: GlobalSetting.try(:saml_cert_fingerprint_algorithm),
                       idp_cert: setting(:cert),
                       request_attributes: request_attributes,
                       attribute_statements: attribute_statements,
                       assertion_consumer_service_url: Discourse.base_url + "/auth/#{name}/callback",
+                      single_logout_service_url: Discourse.base_url + "/auth/#{name}/slo",
                       name_identifier_format: GlobalSetting.try(:saml_name_identifier_format),
                       custom_url: (GlobalSetting.try(:saml_request_method) == 'post') ? "/discourse_saml" : nil,
                       certificate: GlobalSetting.try(:saml_sp_certificate),