fixes for Response.writeError with servlet error dispatch

jetty-core/jetty-security/src/main/java/org/eclipse/jetty/security/AuthenticationState.java

@@ -23,6 +23,7 @@
 import org.eclipse.jetty.security.internal.DeferredAuthenticationState;
 import org.eclipse.jetty.server.Request;
 import org.eclipse.jetty.server.Response;
+import org.eclipse.jetty.server.handler.ErrorHandler;
 import org.eclipse.jetty.util.Callback;
 
 /**
@@ -179,6 +180,19 @@ static boolean logout(Request request, Response response)
         return false;
     }
 
+    static AuthenticationState writeError(Request request, Response response, Callback callback, int code)
+    {
+        if (request.getContext().getErrorHandler() instanceof ErrorHandler errorHandler)
+        {
+            return errorHandler.writeError(request, response, callback, HttpStatus.FORBIDDEN_403)
+                    ? AuthenticationState.SEND_FAILURE 
+                    : new AuthenticationState.ServeAs(request.getHttpURI());
+        }
+
+        Response.writeError(request, response, callback, HttpStatus.FORBIDDEN_403);
+        return AuthenticationState.SEND_FAILURE;
+    }
+
     /**
      * A successful Authentication with User information.
      */

jetty-core/jetty-security/src/main/java/org/eclipse/jetty/security/authentication/BasicAuthenticator.java

@@ -87,6 +87,8 @@ public AuthenticationState validateRequest(Request req, Response res, Callback c
         if (charset != null)
             value += ", charset=\"" + charset.name() + "\"";
         res.getHeaders().put(HttpHeader.WWW_AUTHENTICATE.asString(), value);
+
+        // Don't use AuthenticationState.writeError, to avoid possibility of doing a Servlet error dispatch.
         Response.writeError(req, res, callback, HttpStatus.UNAUTHORIZED_401);
         return AuthenticationState.CHALLENGE;
     }

jetty-core/jetty-security/src/main/java/org/eclipse/jetty/security/authentication/DigestAuthenticator.java

@@ -180,8 +180,9 @@ else if (n == 0)
                     "\", algorithm=MD5" +
                     ", qop=\"auth\"" +
                     ", stale=" + stale);
-            Response.writeError(req, res, callback, HttpStatus.UNAUTHORIZED_401);
 
+            // Don't use AuthenticationState.writeError, to avoid possibility of doing a Servlet error dispatch.
+            Response.writeError(req, res, callback, HttpStatus.UNAUTHORIZED_401);
             return AuthenticationState.CHALLENGE;
         }
 

jetty-core/jetty-security/src/main/java/org/eclipse/jetty/security/authentication/FormAuthenticator.java

@@ -365,7 +365,7 @@ private AuthenticationState dispatch(String path, Request request, Response resp
     private AuthenticationState sendError(Request request, Response response, Callback callback)
     {
         if (_formErrorPage == null)
-            Response.writeError(request, response, callback, HttpStatus.FORBIDDEN_403);
+            return AuthenticationState.writeError(request, response, callback, HttpStatus.FORBIDDEN_403);
         else if (_dispatch)
             return dispatch(_formErrorPage, request, response, callback);
         else

jetty-core/jetty-security/src/main/java/org/eclipse/jetty/security/authentication/SPNEGOAuthenticator.java

@@ -185,6 +185,7 @@ else if (httpSession != null)
     private void sendChallenge(Request req, Response res, Callback callback, String token)
     {
         setSpnegoToken(res, token);
+        // Don't use AuthenticationState.writeError, to avoid possibility of doing a Servlet error dispatch.
         Response.writeError(req, res, callback, HttpStatus.UNAUTHORIZED_401);
     }
 

jetty-core/jetty-security/src/main/java/org/eclipse/jetty/security/authentication/SslClientCertAuthenticator.java

@@ -56,11 +56,8 @@ public String getAuthenticationType()
     public AuthenticationState validateRequest(Request req, Response res, Callback callback) throws ServerAuthException
     {
         if (!(req.getAttribute(EndPoint.SslSessionData.ATTRIBUTE) instanceof EndPoint.SslSessionData sslSessionData))
-        {
-            Response.writeError(req, res, callback, HttpStatus.FORBIDDEN_403);
-            return AuthenticationState.SEND_FAILURE;
-        }
-
+            return AuthenticationState.writeError(req, res, callback, HttpStatus.FORBIDDEN_403);
+
         X509Certificate[] certs = sslSessionData.peerCertificates();
 
         try
@@ -106,10 +103,7 @@ public AuthenticationState validateRequest(Request req, Response res, Callback c
             }
 
             if (!AuthenticationState.Deferred.isDeferred(res))
-            {
-                Response.writeError(req, res, callback, HttpStatus.FORBIDDEN_403);
-                return AuthenticationState.SEND_FAILURE;
-            }
+                return AuthenticationState.writeError(req, res, callback, HttpStatus.FORBIDDEN_403);
 
             return null;
         }

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/handler/ErrorHandler.java

@@ -92,6 +92,28 @@ public boolean errorPageForMethod(String method)
         return ERROR_METHODS.contains(method);
     }
 
+    /**
+     * Write an error response, or signal that the error will be handled by a down stream handler.
+     * <p>
+     * The default implementation calls {@link Response#writeError(Request, Response, Callback, int)} and returns {@code true}.
+     * <p>
+     * <p>
+     * Servlet implementations will override this method to trigger a sendError when the {@code ServletChannel} is started and return {@code false}.
+     * </p>
+     *
+     * @param request  The request.
+     * @param response The response.
+     * @param callback The callback to call when the response is written.
+     * @param code     The error status code.
+     * @return {@code true} if the error response was written; {@code false} if the state of the request and/or response
+     * has been changed so that by continuing normal handling an error response will be generated by a down stream handler.
+     **/
+    public boolean writeError(Request request, Response response, Callback callback, int code)
+    {
+        Response.writeError(request, response, callback, code);
+        return true;
+    }
+
     @Override
     public boolean handle(Request request, Response response, Callback callback) throws Exception
     {

jetty-ee10/jetty-ee10-jaspi/src/main/java/org/eclipse/jetty/ee10/security/jaspi/JaspiAuthenticator.java

@@ -233,8 +233,7 @@ public AuthenticationState validateRequest(JaspiMessageInfo messageInfo) throws
             }
             if (authStatus == AuthStatus.FAILURE)
             {
-                Response.writeError(messageInfo.getBaseRequest(), messageInfo.getBaseResponse(), messageInfo.getCallback(), HttpServletResponse.SC_FORBIDDEN);
-                return AuthenticationState.SEND_FAILURE;
+                return AuthenticationState.writeError(messageInfo.getBaseRequest(), messageInfo.getBaseResponse(), messageInfo.getCallback(), HttpServletResponse.SC_FORBIDDEN);
             }
             // should not happen
             throw new IllegalStateException("No AuthStatus returned");