Hi @BiBo, there is also Forwarded headers - Grist Help Center , which works pretty well in any reverse proxy. And Sign in with getgrist.com - Grist Help Center is very easy to set up if it matches your needs.
@Adrien_PARROT, yes, the original OIDC implementation in Grist was by @Florent_F at ANCT/DINUM. Florent has contributed great things to Grist. See One Grist, one edition, in grist-core for a community analysis of this part.