Experiment with minimal implementation of AxaGuilDEv/react-oidc

[tristan-orourke]

Description

Experiment with implementing simple login with PKCE using AxaGuilDEv/react-oidc. Don't worry about refreshing, or logout, just try to get a basic login working.
While at this, investigate how we could integrate this into our existing frontend auth components.

[petertgiles]

Gonna put this one down for now on Gray's request. Summary so far:

• I have the demo app working with mock auth in this repo: https://github.com/petertgiles/axa-with-mock/tree/first-try
• Seems to work well with Mock Auth
• SiC has problems with CORS on the well-known/configuration page. Doug says they will fix this on their next sprint.
  

[tristan-orourke]

This is no longer necessary, I feel comfortable jumping straight to attempting #4916.