FIX: verify presence of 'sso url' before enabling 'enable sso'

config/locales/server.en.yml

@@ -1615,6 +1615,7 @@ en:
       enable_sso_disabled: "You must first enable 'enable sso' before enabling this setting."
       staged_users_disabled: "You must first enable 'staged users' before enabling this setting."
       reply_by_email_disabled: "You must first enable 'reply by email' before enabling this setting."
+      sso_url_is_empty: "You must set a 'sso url' before enabling this setting."
 
   search:
     within_post: "#%{post_number} by %{username}"

config/site_settings.yml

@@ -291,6 +291,7 @@ login:
   enable_sso:
     client: true
     default: false
+    validator: "EnableSsoValidator"
   sso_allows_all_return_paths: false
   enable_sso_provider: false
   verbose_sso_logging: false

lib/validators/enable_sso_validator.rb

@@ -0,0 +1,14 @@
+class EnableSsoValidator
+  def initialize(opts = {})
+    @opts = opts
+  end
+
+  def valid_value?(val)
+    return true if val == 'f'
+    SiteSetting.sso_url.present?
+  end
+
+  def error_message
+    I18n.t('site_settings.errors.sso_url_is_empty')
+  end
+end

spec/components/validators/enable_sso_validator_spec.rb

@@ -0,0 +1,48 @@
+require 'rails_helper'
+
+RSpec.describe EnableSsoValidator do
+  subject { described_class.new }
+
+  describe '#valid_value?' do
+    describe "when 'sso url' is empty" do
+      before do
+        SiteSetting.sso_url = ""
+      end
+
+      describe 'when val is false' do
+        it 'should be valid' do
+          expect(subject.valid_value?('f')).to eq(true)
+        end
+      end
+
+      describe 'when value is true' do
+        it 'should not be valid' do
+          expect(subject.valid_value?('t')).to eq(false)
+
+          expect(subject.error_message).to eq(I18n.t(
+            'site_settings.errors.sso_url_is_empty'
+          ))
+        end
+      end
+    end
+
+    describe "when 'sso url' is present" do
+      before do
+        SiteSetting.sso_url = "https://www.example.com/sso"
+      end
+
+      describe 'when value is false' do
+        it 'should be valid' do
+          expect(subject.valid_value?('f')).to eq(true)
+        end
+      end
+
+      describe 'when value is true' do
+        it 'should be valid' do
+          expect(subject.valid_value?('t')).to eq(true)
+        end
+      end
+    end
+
+  end
+end