Legacy kibana-auth-plugin have to be migrated to the Kibana Platform

[kinjelom]

Kibana 7.10.0+:

The legacy plugin system and the legacy plugin API have been removed. It is no longer possible to use third parties legacy Kibana plugins. Legacy plugin owners should migrate their plugins to the Kibana Platform plugin API

https://www.elastic.co/guide/en/kibana/7.10/release-notes-7.10.0.html

• Migrating legacy plugins to the Kibana Platform: https://www.elastic.co/guide/en/kibana/current/migrating-legacy-plugins.html
• Migration examples: https://www.elastic.co/guide/en/kibana/current/migrating-legacy-plugins-examples.html#migrating-legacy-plugins-examples