If you are trying to use SAML authentication to log in to SimpleRisk by clicking the "Go to SSO Login Page" link, you may find yourself with a message like this:
[Tue Jan 15 20:03:13.620564 2019] [:error] [pid 22300] [client 70.114.131.253:54990] PHP Fatal error: Uncaught Error: Class 'DOMDocument' not found in /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/vendor/simplesamlphp/saml2/src/SAML2/DOMDocumentFactory.php:96\nStack trace:\n#0 /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/vendor/simplesamlphp/saml2/src/SAML2/DOMDocumentFactory.php(24): SAML2_DOMDocumentFactory::create()\n#1 /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/lib/SimpleSAML/Metadata/SAMLParser.php(331): SAML2_DOMDocumentFactory::fromString('<?xml version="...')\n#2 /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/saml-autoconfig.php(51): SimpleSAML_Metadata_SAMLParser::parseDescriptorsString('<?xml version="...')\n#3 /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/config/authsources.php(67): require('/var/www/dev.si...')\n#4 /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/lib/SimpleSAML/Configuration.php(114): require in /var/www/dev.simplerisk.org/www/simplerisk/extras/authentication/simplesamlphp/vendor/simplesamlphp/saml2/src/SAML2/DOMDocumentFactory.php on line 96
If you receive this message under this scenario, the issue is that the php-dom module is not installed on your server. To install it, run the following commands:
sudo apt-get install php-dom
sudo service apache2 restart