Redirect Loops
A redirect loop can occur when a user tries to authenticate with SSO/SAML but because of the presence of a cache or CDN which is not set to bypass the cache on the presence of the SAML cookie(s). SimpleSAMLPHP uses a cookie starting with 'SimpleSAML', so bypasing the cache for 'SimpleSAML.*' should avoid any issues. See below for an example Page Rule
Redirect loops can also be caused by a redirect switching from http to https, refer to the SimpleSAMLphp debugging documentation as well as the Troubleshooting SimpleSAML article.