Access OpenId-Connect IDP via Keycloak with additional Basic Auth

Greetings everyone,

We are currently evaluating the possibilities of keycloak since we need to replace a custom SSO solution. This requires us to connect to external IDPs which we already connected to.

Currently I am investigating an OpenID-Connect Provider which is authenticating the clients via POST using client_id and client_secret as parameters. Additionally, its API is secured with a basic authentication via the Authorization header. Whilst the first part is no problem, I have not found a solution to overcome the additional basic authentication with the available default configurations (using a user-defined OpenID Connect V1.0 provider). Vice versa, I can overcome the basic authentication, but then will miss the client_id and client_secret parameters which results in an error of the IDP not returning an access token.

Is there a way to resolve this issue? If not via default options, is there an option to add custom IDPs which can be configured in the backend? I saw the SPIs in the developer documentation ( but I am not sure if one of those suits our needs.