Identity | Add instructions on developing with okta/sign in local dev

[coldlink]

What does this change?

For Frontend local development we want to be able to use Okta/OAuth tokens locally during development to test and develop against signed in features.

This is currently very difficult as Frontend developments happens on localhost, which cannot share cookies with Identity/Okta, which runs on https on the profile subdomain.

However Fronend can be run on https://m.thegulocal.com by following these instructions. Since that does run locally using https, and on the thegulocal.com domain, it makes it possible to share cookies with Okta.

This PR updates those instructions with updated ones showing exactly the steps needed to be taken in order to enable this. It also updates @guardian/identity-auth-frontend which enables the use of this domain in local development (see the CSNX and Identity Platform PRs below).

Related PRs

Identity Platform: https://github.com/guardian/identity-platform/pull/802
Dotcom Rendering: guardian/dotcom-rendering#13426
CSNX: guardian/csnx#1964
Frontend (This PR): #27791

Tested

• Local DEV

[github-actions]

Deploy build 3911 of dotcom:frontend-all to CODE

All deployment options

• Deploy build 3911 of dotcom:frontend-all to CODE
• Deploy parts of build 3911 to CODE by previewing it first
• What's on CODE right now?

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From guardian/actions-riff-raff.