@Override
    public void initialize(Subject subject, CallbackHandler callbackHandler, Map<String, ?> sharedState,
            Map<String, ?> options) {
        this.subject = Objects.requireNonNull(subject);
        if (!(Objects.requireNonNull(callbackHandler) instanceof AuthenticateCallbackHandler))
            throw new IllegalArgumentException(String.format("Callback handler must be castable to %s: %s",
                    AuthenticateCallbackHandler.class.getName(), callbackHandler.getClass().getName()));
        this.callbackHandler = (AuthenticateCallbackHandler) callbackHandler;
    }
The SASL Mechanism name for OAuth 2: {@code OAUTHBEARER}
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/OAuthBearerLoginModule.java