Add authentik to SSO (#498)

Co-authored-by: nodiscc <nodiscc@gmail.com>

README.md

@@ -436,6 +436,7 @@ _Related: [DNS - Servers](#dns---servers)_
 **[`^        back to top        ^`](#awesome-sysadmin)**
 
 - [Authelia](https://www.authelia.com/) - The Single Sign-On Multi-Factor portal for web apps. ([Source Code](https://github.com/authelia/authelia)) `Apache-2.0` `Go`
+- [Authentik](https://goauthentik.io/) - Flexible identity provider with support for different protocols. (OAuth 2.0, SAML, LDAP and Radius). ([Source Code](https://github.com/goauthentik/authentik)) `MIT` `Python`
 - [KeyCloak](https://www.keycloak.org) - Open Source Identity and Access Management. ([Source Code](https://github.com/keycloak/keycloak)) `Apache-2.0` `Java`