How to handle missing redirect_uri in token request for Keycloak OAuth integration?

[StopDragon]

I'm integrating Naver Works with Keycloak via OAuth 2.0 using the authorization_code grant.
The login flow fails during the /token exchange with the following Keycloak error:

2025-04-30 11:56:26,668 WARN [org.keycloak.events] (executor-thread-28) type="CODE_TO_TOKEN_ERROR", realmId="4e3e9cab-a720-4807-a247-14c5164eb0ec", realmName="*****", clientId="*****", userId="1e84e1c4-cc76-4448-8451-77c18c012dd3", sessionId="9c4d4a81-ccc3-49c9-b408-7f52731ab1bf", ipAddress="*********", error="invalid_redirect_uri", reason="Parameter 'redirect_uri' did not match originally saved redirect URI used in initial OIDC request. Saved redirectUri: https://auth.worksmobile.com/view/oauth/sso/authorization/U44BZ771, redirectUri parameter: null", grant_type="authorization_code", code_id="9c4d4a81-ccc3-49c9-b408-7f52731ab1bf", client_auth_method="client-secret"

error="invalid_redirect_uri", reason="Parameter 'redirect_uri' did not match originally saved redirect URI used in initial OIDC request. Saved redirectUri: ..., redirectUri parameter: null"
However, Naver Works does not include redirect_uri in its token request by design, and this behavior cannot be changed.
This causes Keycloak to reject the token exchange due to strict matching of the redirect_uri.

Attempts so far:

Valid Redirect URIs set to * in Keycloak → still fails

Keycloak version: 26.x

Cannot change Naver Works behavior

What I'm looking for:

Any official or supported workaround in Keycloak (e.g., relaxing redirect_uri validation)?

Can I use a reverse proxy or Cloudflare Worker to inject the redirect_uri before the token request reaches Keycloak?

Is it possible to extend or customize Keycloak behavior for this specific client?

Thanks in advance.