Comment on page
In Flow the connection can either be set up as it's own connector (External Oauth2 provider), or set it up within the Rest-connector itself. This is an example with Flow set up against Salesforce with 5 input parameters (string). The response is captured under the OK response.
Salesforce example with Oauth2
If you choose to set up the authentication with the Oauth2-connector it may look like this which is an example of a connection with Microsoft Office 365