Function render_sso_options 

fn render_sso_options<'a, I>(
    heading: &str,
    req_id: &str,
    providers: I,
) -> String
where
    I: IntoIterator<Item = (&'a str, &'a str)>,

List each provider as a link that binds the pending request to it.

Names are HTML-escaped with braces encoded too, since the result is filled in before the error and context placeholders.