Sign into ON API using Blackbaud Account

I am developing an application for an environment that uses the ON API. This environment switched to using Blackbaud Accounts for sign-in, but it still uses the ON api. How do I get an ON token using a Sky OAuth2 token? I can get a token and the application is linked. The school website is capable of logging into the ON API application, I can't find anything in the documentation explaining how to do this.