Issue with Refreshing Access Tokens in Sling OAuth Integration

[r0xsh]

The initial OAuth process to obtain an access token works as expected, and we are able to interact with Sling's API using the provided access token. However, we have encountered an issue with the token refresh mechanism. After the access token expires, there appears to be no endpoint or method available to use the refresh_token to obtain a new access token.

Steps to Reproduce

1. Obtain an initial access token by sending a POST request to https://api.getsling.com/oauth2/token with the necessary authentication details.
2. Use the access token to make authenticated requests to Sling's API until the token expires (usually after 3600 seconds).
3. Attempt to use the refresh_token provided in the initial response to obtain a new access token.

Expected Behavior

There should be a clear method or endpoint (typically something like /oauth2/token with a grant_type of refresh_token) to submit the refresh_token and receive a new access token without requiring the user to re-authenticate.

See: https://www.oauth.com/oauth2-servers/access-tokens/refreshing-access-tokens/

Actual Behavior

Currently, there is no documented or apparent way to use the refresh_token to obtain a new access token once the initial token has expired.