Function fetch_oauth2_token 

pub async fn fetch_oauth2_token(
    token_url: &str,
    client_id: &str,
    client_secret: &str,
    scopes: &[String],
) -> Result<String, FaucetError>

Available on crate feature source-rest only.

Fetch an OAuth2 token using the client credentials grant.

Prefer using TokenCache::get_or_refresh to avoid fetching a new token on every request.