output: #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;
      }
input: #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 34 
                              #vulnerability type NULL_DEREFERENCE