Function attach_credential 

pub fn attach_credential(
    task: &mut Value,
    hook_name: &str,
    extensions: &Extensions,
    capabilities: &HashSet<String>,
) -> Result<(), HostError>

Attach the credential object to a task, when the hook and the plugin’s declared capabilities both call for it.

A no-op for every hook other than identity.resolve and token.delegate, and for any plugin that declared neither capability.