Add Medium article

Author: Ivan Franchin

README.md

@@ -11,6 +11,7 @@ On [ivangfr.github.io](https://ivangfr.github.io), I have compiled my Proof-of-C
 - \[**Medium**\] [**Implementing and Securing a Simple Spring Boot REST API with Okta**](https://medium.com/javarevisited/implementing-and-securing-a-simple-spring-boot-rest-api-with-okta-a5143696cd60)
 - \[**Medium**\] [**Implementing and Securing a Simple Spring Boot UI (Thymeleaf + RBAC) with Okta**](https://medium.com/javarevisited/implementing-and-securing-a-simple-spring-boot-ui-thymeleaf-rbac-with-okta-9489cbbcec25)
 - \[**Medium**\] [**Implementing and Securing a Spring Boot GraphQL API with Okta**](https://medium.com/javarevisited/implementing-and-securing-a-spring-boot-graphql-api-with-okta-78bc997359b4)
+- \[**Medium**\] [**Building a Single Spring Boot App with Keycloak or Okta as IdP: Introduction**](https://medium.com/@ivangfr/building-a-single-spring-boot-app-with-keycloak-or-okta-as-idp-introduction-2814a4829aed)
 
 ## Project User Interface Preview