#vulnerable code 
                                @Override
    public AuthenticationMechanismOutcome authenticate(HttpServerExchange exchange, SecurityContext securityContext) {
        BearerTokenAuthenticator bearer = createBearerTokenAuthenticator();
        AuthenticationMechanismOutcome outcome = bearer.authenticate(exchange);
        if (outcome == AuthenticationMechanismOutcome.NOT_AUTHENTICATED) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, bearer.getChallenge());
            return AuthenticationMechanismOutcome.NOT_AUTHENTICATED;
        }
        else if (outcome == AuthenticationMechanismOutcome.AUTHENTICATED) {
            final AccessToken token = bearer.getToken();
            String surrogate = bearer.getSurrogate();
            KeycloakAuthenticatedSession session = new KeycloakAuthenticatedSession(bearer.getTokenString(), token, resourceMetadata);
            KeycloakPrincipal principal = completeAuthentication(securityContext, token, surrogate);
            propagateBearer(exchange, session, principal);
            return AuthenticationMechanismOutcome.AUTHENTICATED;
        }
        else if (adapterConfig.isBearerOnly()) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, bearer.getChallenge());
            return AuthenticationMechanismOutcome.NOT_ATTEMPTED;
        }

        OAuthAuthenticator oauth = createOAuthAuthenticator(exchange);
        outcome = oauth.authenticate();
        if (outcome == AuthenticationMechanismOutcome.NOT_AUTHENTICATED) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, oauth.getChallenge());
            return AuthenticationMechanismOutcome.NOT_AUTHENTICATED;
        }
        else if (outcome == AuthenticationMechanismOutcome.NOT_ATTEMPTED) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, oauth.getChallenge());
            return AuthenticationMechanismOutcome.NOT_ATTEMPTED;

        }
        KeycloakAuthenticatedSession session = new KeycloakAuthenticatedSession(oauth.getTokenString(), oauth.getToken(), resourceMetadata);
        KeycloakPrincipal principal = completeAuthentication(securityContext, oauth.getToken(), null);
        propagateOauth(exchange, session, principal);
        log.info("AUTHENTICATED");
        return AuthenticationMechanismOutcome.AUTHENTICATED;
    } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public AuthenticationMechanismOutcome authenticate(HttpServerExchange exchange, SecurityContext securityContext) {
        BearerTokenAuthenticator bearer = createBearerTokenAuthenticator();
        AuthenticationMechanismOutcome outcome = bearer.authenticate(exchange);
        if (outcome == AuthenticationMechanismOutcome.NOT_AUTHENTICATED) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, bearer.getChallenge());
            return AuthenticationMechanismOutcome.NOT_AUTHENTICATED;
        }
        else if (outcome == AuthenticationMechanismOutcome.AUTHENTICATED) {
            completeAuthentication(securityContext, bearer);
            return AuthenticationMechanismOutcome.AUTHENTICATED;
        }
        else if (adapterConfig.isBearerOnly()) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, bearer.getChallenge());
            return AuthenticationMechanismOutcome.NOT_ATTEMPTED;
        }

        OAuthAuthenticator oauth = createOAuthAuthenticator(exchange);
        outcome = oauth.authenticate();
        if (outcome == AuthenticationMechanismOutcome.NOT_AUTHENTICATED) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, oauth.getChallenge());
            return AuthenticationMechanismOutcome.NOT_AUTHENTICATED;
        }
        else if (outcome == AuthenticationMechanismOutcome.NOT_ATTEMPTED) {
            exchange.putAttachment(KEYCLOAK_CHALLENGE_ATTACHMENT_KEY, oauth.getChallenge());
            return AuthenticationMechanismOutcome.NOT_ATTEMPTED;

        }
        completeAuthentication(securityContext, oauth);
        log.info("AUTHENTICATED");
        return AuthenticationMechanismOutcome.AUTHENTICATED;
    }