I am experiencing the same issue. Front channel is not an option because my IDP client has a strict setup for the authorization code flow only. However, when I initiate the back channel, which supports code flow. I always receive the error: “invalid_client (Client authentication failed. Either the client or the client credentials are invalid).”
It seems like public IDP clients are not supported for the authorization code flow with PKCE. Is this correct?
Thank you.