Function create_auth_cookie 

pub fn create_auth_cookie(
    options: &RustAuthOptions,
    name: &str,
    max_age: Option<u64>,
) -> Result<AuthCookie, RustAuthError>

Build a single auth cookie definition using the same name prefixing and attribute merge policy as get_cookies.

Plugins should route their own security-sensitive cookies (for example the passkey challenge cookie) through this helper so they inherit the configured cookie_prefix, secure-name prefix, cross-subdomain domain, and default_cookie_attributes instead of using a raw, unnamespaced cookie name.