Bypass asset_host configuration for icon sprite

[aduth]

Why: Icon sprites consumed via SVG <use> cannot reference cross-domain resources, so it must be served from the same host.

Related Slack discussion: https://gsa-tts.slack.com/archives/C0NGESUN5/p1643749421139809

[aduth]

This comes from the fallback here:

identity-idp/config/environments/production.rb

Line 11 in efa5c49

(IdentityConfig.store.asset_host.presence || IdentityConfig.store.domain_name) if request

[zachmargolis]

this branch is not covered by tests, I'd consider adding it

if we don't want to stub Rails.env, we could do some dependency injection:

def asset_host(rails_env = Rails.env)
  if rails_env.production?

and then in the test pass in a ActiveSupport::EnvironmentInquirer.new("production") or ActiveSupport::EnvironmentInquirer.new("development") etc

[aduth]

this branch is not covered by tests, I'd consider adding it

👍 Added specs in rebased 8f82e3b.

Went for stubbing due to light preference to keep asset_host a private method.

[aduth]

...and this matches the default behavior of Rails asset URL calculation:

https://github.com/rails/rails/blob/d35bcc93f791b9be7a41905c6342f9044b24f298/actionview/lib/action_view/helpers/asset_url_helper.rb#L292

[zachmargolis]

LGTM

[aduth]

Confirmed that this works in my personal sandbox, which otherwise uses a CDN for assets: