Custom Auth Flow not giving back all data

I am trying to get an OAuth2.0 flow that triggers a series of workflows after the user completes the authentication.

To date, I have used the Custom Auth Flows for this and it has worked perfectly.

I am now looking at connecting to a different API. This has a default connection address to generate the tokens, but after that all api requests have to be posted to an address specific to the connection. {{connection_name}} for example. This will change with each connection.

Now, when I do a normal OAuth2.0 flow (not custom) I do get this data back as a sanitised line in the response.
If I do a custom Auth, then use the OAuth2 (Generic) function, I only get returned the accessToken and refreshToken.

Is there something obvious that I am missing?

What would be the most effective way to trigger a workflow that will make an API call to the "endpoint" returned from the Auth call?