Function refresh_access_token 

pub async fn refresh_access_token(
    http: &Client,
    token_url: &str,
    client_id: &str,
    refresh_token: &str,
) -> Result<TokenResponse, TokenError>

Refreshes an access token and returns the raw TokenResponse (rotation-aware: callers read refresh_token off the response).

Errors

TokenError::Status when the refresh is rejected (revoked/expired).