Just released 0.2.0 of Kotlin oauth2 server:
https://github.com/adhesivee/kotlin-oauth2-server
The following have been improved/introduced:
• Support for Sparkjava
• Support for custom authentication instead of default http basic authentication
• Support for authorized grant types per client
• Core structure improvements to easier implement new frameworks
• Improve oauth2 error handling
• TokenStore now allows revoking tokens