How can I modify response_type to OIDC Authentication Request

*Description*:
>Describe the issue.
according to https://github.com/envoyproxy/gateway/issues/5133 I could do following to add and modify request uri:
```
/authorize?
&code_challenge_method=S256
&response_type=code%20idtoken

```
I switched code_challenge_method back and forth from plain to S256, both show up in request Uri
but no matter what I change response_type to, "response_type=code" always shows up in request uri.

Any workaround to that?

>settings:
```yaml
oidc:
provider:
issuer: "https://keycloak.home-domain.com/identity"
authorizationEndpoint: "https://keycloak.home-domain.com/identity/connect/authorize?code_challenge_method=plain&response_type=codeblanc"
tokenEndpoint: "https://keycloak.home-domain.com/identity/connect/token"
clientID: "gw"
clientSecret:
name: "secret"
redirectURL: "https://app.home-domain.com/auth"
logoutPath: "/SignedOut"
```