If you read this Using Spring Security OAuth 2.0 and MongoDB For Single Sign Authentication Server. This is just building on it to get a single sign on microservice with LDAP integration.
The main focus of this is explore the functionality of AuthenticationProvider in Spring Security
Read more here.
You can use the client service I wrote to test this. The major changes worked on in this project are in the auth-server. Which now supports LDAP for authentication.