Bael 6188: Extract CN from X509Certificate in Java (#14681)

* #BAEL-6188:add unit tests

* #BAEL-6188:add dependencies

* #BAEL-6188:add certificate

* #BAEL-6188:add extract CN using Regex

* #BAEL-6188:refactor CN using Regex

* #BAEL-6188:refactor test case name

* #BAEL-6188:add properties for dependency version

core-java-modules/core-java-security-4/pom.xml

@@ -13,4 +13,22 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.bouncycastle</groupId>
+            <artifactId>bcpkix-jdk15on</artifactId>
+            <version>${bouncycastle.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.cryptacular</groupId>
+            <artifactId>cryptacular</artifactId>
+            <version>${cryptacular.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <bouncycastle.version>1.70</bouncycastle.version>
+        <cryptacular.version>1.2.6</cryptacular.version>
+    </properties>
+
 </project>

core-java-modules/core-java-security-4/src/main/resources/Baeldung.cer

@@ -0,0 +1,20 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

core-java-modules/core-java-security-4/src/test/java/com/baeldung/certificate/ExtractCommonNameUnitTest.java

@@ -0,0 +1,94 @@
+package com.baeldung.certificate;
+
+import org.bouncycastle.asn1.x500.RDN;
+import org.bouncycastle.asn1.x500.X500Name;
+import org.bouncycastle.asn1.x500.style.BCStyle;
+import org.bouncycastle.asn1.x500.style.IETFUtils;
+import org.bouncycastle.jce.provider.BouncyCastleProvider;
+import org.cryptacular.util.CertUtil;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import javax.naming.ldap.LdapName;
+import javax.naming.ldap.Rdn;
+import javax.security.auth.x500.X500Principal;
+import java.io.FileInputStream;
+import java.security.Security;
+import java.security.cert.CertificateFactory;
+import java.security.cert.X509Certificate;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ExtractCommonNameUnitTest {
+
+    private static final String EXPECTED_CN = "Baeldung";
+
+    private String certificatePath = "src/main/resources/Baeldung.cer";
+
+    private X509Certificate certificate;
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        Security.addProvider(new BouncyCastleProvider());
+        CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509", "BC");
+        certificate = (X509Certificate) certificateFactory.generateCertificate(new FileInputStream(certificatePath));
+    }
+
+    @Test
+    void whenUsingBouncyCastle_thenExtractCommonName() {
+        X500Principal principal = certificate.getSubjectX500Principal();
+        X500Name x500Name = new X500Name(principal.getName());
+        RDN[] rdns = x500Name.getRDNs(BCStyle.CN);
+        List<String> names = new ArrayList<>();
+        for (RDN rdn : rdns) {
+            String name = IETFUtils.valueToString(rdn.getFirst().getValue());
+            names.add(name);
+        }
+
+        for (String commonName : names) {
+            assertEquals(EXPECTED_CN, commonName);
+        }
+    }
+
+    @Test
+    void whenUsingLDAPAPI_thenExtractCommonName() throws Exception {
+        X500Principal principal = certificate.getSubjectX500Principal();
+        LdapName ldapDN = new LdapName(principal.getName());
+        List<String> names = new ArrayList<>();
+        for (Rdn rdn : ldapDN.getRdns()) {
+            if (rdn.getType().equalsIgnoreCase("cn")) {
+                String name = rdn.getValue().toString();
+                names.add(name);
+            }
+        }
+
+        for (String commonName : names) {
+            assertEquals(EXPECTED_CN, commonName);
+        }
+    }
+
+    @Test
+    void whenUsingCryptacular_thenExtractCommonName() {
+        String commonName = CertUtil.subjectCN(certificate);
+        assertEquals(EXPECTED_CN, commonName);
+    }
+
+    @Test
+    void whenUsingRegex_thenExtractCommonName() {
+        X500Principal principal = certificate.getSubjectX500Principal();
+        List<String> names = new ArrayList<>();
+        Pattern pattern = Pattern.compile("CN=([^,]+)");
+        Matcher matcher = pattern.matcher(principal.getName());
+        while (matcher.find()) {
+            names.add(matcher.group(1));
+        }
+
+        for (String commonName : names) {
+            assertEquals(EXPECTED_CN, commonName);
+        }
+    }
+}