Update help/instance_configuration: hide SSH keys if algorithm disabled

app/models/instance_configuration.rb

@@ -22,7 +22,12 @@ class InstanceConfiguration
   private
 
   def ssh_algorithms_hashes
-    SSH_ALGORITHMS.map { |algo| ssh_algorithm_hashes(algo) }.compact
+    SSH_ALGORITHMS.select { |algo| ssh_algorithm_enabled?(algo) }.map { |algo| ssh_algorithm_hashes(algo) }.compact
+  end
+
+  def ssh_algorithm_enabled?(algorithm)
+    algorithm_key_restriction = application_settings["#{algorithm.downcase}_key_restriction"]
+    algorithm_key_restriction.nil? || algorithm_key_restriction != ApplicationSetting::FORBIDDEN_KEY_VALUE
   end
 
   def host

spec/models/instance_configuration_spec.rb

@@ -31,6 +31,23 @@ RSpec.describe InstanceConfiguration do
           expect(result.size).to eq(InstanceConfiguration::SSH_ALGORITHMS.size)
         end
 
+        it 'includes all algorithms' do
+          stub_pub_file(pub_file)
+
+          result = subject.settings[:ssh_algorithms_hashes]
+
+          expect(result.map { |a| a[:name] }).to match_array(%w(DSA ECDSA ED25519 RSA))
+        end
+
+        it 'does not include disabled algorithm' do
+          Gitlab::CurrentSettings.current_application_settings.update!(dsa_key_restriction: ApplicationSetting::FORBIDDEN_KEY_VALUE)
+          stub_pub_file(pub_file)
+
+          result = subject.settings[:ssh_algorithms_hashes]
+
+          expect(result.map { |a| a[:name] }).to match_array(%w(ECDSA ED25519 RSA))
+        end
+
         def pub_file(exist: true)
           path = exist ? 'spec/fixtures/ssh_host_example_key.pub' : 'spec/fixtures/ssh_host_example_key.pub.random'