OAUTH 2.0 - Authorization Code Flow

I am using kong 0.13.1. Is there any documentation available to integrate OAUTH Authorization Code flow in a service instead of APIs.

You only need to enable the plugin on a Service entity instead of an API entity: this is an example from the documentation using a Service:

Configure this plugin on a Service by making the following request:

$ curl -X POST http://kong:8001/services/{my_service}/plugins \
    --data "name=oauth2"  \
    --data "config.scopes=email,phone,address" \
    --data "config.mandatory_scope=true" \
    --data "config.enable_authorization_code=true"

More about it here: https://docs.konghq.com/plugins/oauth2-authentication/