This is a second part authentiction. this method if you already have been authenticate the API and already have a refresh_token valid
To get a access_token from plugin authetication method you need 4 credencials.
- client_id - Plugin API id
- client_secret - Plugin API password
- refresh_token - RefreshToken Keeped
- grant_type - refresh_token
IMPORTANT Every time that you authenticatea new refresh_token is generate that is valid for just few calls, you must keep in your database.