Connect custom SSO with PKCE flow

I’m trying to connect to auth0 a 3rd party SSO solution which only implements PKCE flow. My app already works with Auth0 and I want all my authentication and authorization to be handled through Auth0.

I was trying to do that by creating Authentication->Enterprise->Open ID Connect connection. I was able to configure it using “Front Channel” as I only have client id (client secret is not used by the SSO and is not required for PKCE) However it is not working properly. It fails on the loggin screen just after clicking the button specific to the new connection. The error is: “Required String parameter ‘code_challenge’ is not present”.

Am I doing something wrong or it is not possible to use PKCE in this way?

Best regards
Łukasz Głaz