PKCE support

[schlichtanders]

PKCE is the new recommended flow to replace implicit flow in order to reduce security risks associated with leaking the secret key.

Is PKCE already supported? If not, can you make a sketch on how to support it in OpenIDConnect.jl?
(I am very motivated to get PKCE workflow running in Julia.

Here some further information on PKCE

• https://oauth.net/2/pkce/
• https://www.adaltas.com/en/2020/11/20/oauth-microservices-public-app/

[danlooo]

I have a working proof of concept of OIDC device flow + discovery + PKCE at Open-EO/openeo-julia-client#5 (comment)