Configuring traditional authentication set client_id but kept any
existing client_secret, for example one left in the config from legacy
authentication with a machine specific API key. Whitelabel services
that have moved to an Ory Hydra based identity provider, such as elkjop
and elko, reject a client secret for their public clients, so the token
exchange failed with:
invalid_client: The OAuth 2.0 Client supports client authentication
method 'none', but method 'client_secret_post' was requested.
Clear client_secret, as standard authentication already does.