Does Magento support Just-In-Time Provisioning SAML 2.0 for Magento version 1.3? This would work by using SAML assertion to create users on the fly the first time they try to log in. This eliminates the need to create user accounts in advance.
This extension adds SAML support and has the Just-in-time provisioning feature:- https://marketplace.magento.com/sixtomartin-onelogin-module-saml2.html
For Mage 1.X use:- https://cmsmart.net/magento-extensions/sixto-martin-saml-single-sign-on-magento-extension