Update apache.santuario.xmlsec dep from 2.1.4 to 2.2.6 (#112022)

apache.santuario.xmlsec version 2.1.4 is documented vulnerable.
We should update to mitigate the vulnerabilities.
But apache.santuario.xmlsec is a dependency of opensaml version 3.*.

However, in a patch release of elasticsearch (i.e. 7.17.*) it's best we avoid updating dependencies across major versions (i.e. opensaml from version 3.* to version 4.*), particularly for such a complex dependency as opensaml (we did update the opensaml dep in this way, but in a minor elasticsearch 8.* release, i.e. #98199). The latest opensaml 3.* release (i.e. 3.4.6) still requires a vulnerable apache.santuario.xmlsec dep: https://mvnrepository.com/artifact/org.opensaml/opensaml-xmlsec-impl/3.4.6).

In this case, our best hope is to find a non-vulnerable version of apache.santuario.xmlsec that is still on the same major version as the version listed in the deps of opensaml (i.e. 2.*). That's version 2.2.6: https://mvnrepository.com/artifact/org.apache.santuario/xmlsec/2.2.6 , which is not vulnerable

This PR updates apache.santuario.xmlsec from the existing 2.1.4 version to the 2.2.6 version. The release notes of the 2.2.0 version from https://santuario.apache.org/javareleasenotes.html look simple, and the dependencies differences (from https://mvnrepository.com/artifact/org.apache.santuario/xmlsec/2.1.4) are minimal as well (hopefully optional dependencies, which we don't pull in, stay optional in the same way in the new version).
So, it looks to me that the dep update is relatively safe (and it also passes CI)!

gradle/verification-metadata.xml

@@ -3137,9 +3137,9 @@
             <sha256 value="71f61f34db5e6d926cb8050709fed0ef32788d3f4e9dc06e884c6f3b911b21eb" origin="Generated by Gradle"/>
          </artifact>
       </component>
-      <component group="org.apache.santuario" name="xmlsec" version="2.1.4">
-         <artifact name="xmlsec-2.1.4.jar">
-            <sha256 value="2e2ec8fe0cf873979f630ae4d35e7ede3390321279b7a15de9deed3f3430990c" origin="Generated by Gradle"/>
+      <component group="org.apache.santuario" name="xmlsec" version="2.2.6">
+         <artifact name="xmlsec-2.2.6.jar">
+            <sha256 value="9325edf9e2449a31315b7f0c49204840d465b38f7e83ecc9471da125ea3d5b75" origin="Generated by Gradle"/>
          </artifact>
       </component>
       <component group="org.apache.servicemix.bundles" name="org.apache.servicemix.bundles.antlr" version="2.7.7_5">

x-pack/plugin/identity-provider/build.gradle

@@ -33,7 +33,7 @@ dependencies {
   api "org.opensaml:opensaml-storage-api:3.4.5"
   api "org.opensaml:opensaml-storage-impl:3.4.5"
   api "net.shibboleth.utilities:java-support:7.5.1"
-  api "org.apache.santuario:xmlsec:2.1.4"
+  api "org.apache.santuario:xmlsec:2.2.6"
   api "io.dropwizard.metrics:metrics-core:3.2.2"
   api ("org.cryptacular:cryptacular:1.2.4") {
       exclude group: 'org.bouncycastle'

x-pack/plugin/security/build.gradle

@@ -53,7 +53,7 @@ dependencies {
   api "org.opensaml:opensaml-storage-api:3.4.5"
   api "org.opensaml:opensaml-storage-impl:3.4.5"
   api "net.shibboleth.utilities:java-support:7.5.1"
-  api "org.apache.santuario:xmlsec:2.1.4"
+  api "org.apache.santuario:xmlsec:2.2.6"
   api "io.dropwizard.metrics:metrics-core:3.2.2"
   api ("org.cryptacular:cryptacular:1.2.4") {
     exclude group: 'org.bouncycastle'

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/saml/SamlObjectHandler.java

@@ -11,6 +11,7 @@
 import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.elasticsearch.ElasticsearchSecurityException;
 import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.hash.MessageDigests;
 import org.elasticsearch.core.CheckedFunction;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.TimeValue;
@@ -27,6 +28,7 @@
 import org.opensaml.saml.security.impl.SAMLSignatureProfileValidator;
 import org.opensaml.security.credential.Credential;
 import org.opensaml.security.x509.X509Credential;
+import org.opensaml.xmlsec.algorithm.AlgorithmSupport;
 import org.opensaml.xmlsec.crypto.XMLSigningUtil;
 import org.opensaml.xmlsec.encryption.support.ChainingEncryptedKeyResolver;
 import org.opensaml.xmlsec.encryption.support.EncryptedKeyResolver;
@@ -167,6 +169,21 @@ void validateSignature(Signature signature) {
 
         checkIdpSignature(credential -> {
             try {
+                final String signatureAlg = AlgorithmSupport.getKeyAlgorithm(signature.getSignatureAlgorithm());
+                final String keyAlg = credential.getPublicKey().getAlgorithm();
+                if (signatureAlg != null && signatureAlg.equals(keyAlg) == false) {
+                    if (logger.isDebugEnabled()) {
+                        String keyFingerprint = "SHA265:"
+                            + MessageDigests.toHexString(MessageDigests.sha256().digest(credential.getPublicKey().getEncoded()));
+                        logger.debug(
+                            "Skipping [{}] key [{}] because it is not compatible with signature algorithm [{}]",
+                            keyAlg,
+                            keyFingerprint,
+                            signatureAlg
+                        );
+                    }
+                    return false;
+                }
                 return AccessController.doPrivileged((PrivilegedExceptionAction<Boolean>) () -> {
                     try (RestorableContextClassLoader ignore = new RestorableContextClassLoader(SignatureValidator.class)) {
                         SignatureValidator.validate(signature, credential);