Fix SpnegoEngine.getCompleteServicePrincipalName when servicePrincipalName is not specified. (AsyncHttpClient#1588)

* fix when servicePrincipalName is not specified.

* unit test the fix.

Author: nddipiazza

client/src/main/java/org/asynchttpclient/spnego/SpnegoEngine.java

@@ -256,18 +256,18 @@ public String generateToken(String host) throws SpnegoEngineException {
     }
   }
 
-  protected String getCompleteServicePrincipalName(String host) {
+  String getCompleteServicePrincipalName(String host) {
     String name;
     if (servicePrincipalName == null) {
       if (useCanonicalHostname) {
         host = getCanonicalHostname(host);
       }
-      name = "HTTP/" + host;
+      name = "HTTP@" + host;
     } else {
       name = servicePrincipalName;
-    }
-    if (realmName != null) {
-      name += "@" + realmName;
+      if (realmName != null && !name.contains("@")) {
+        name += "@" + realmName;
+      }
     }
     log.debug("Service Principal Name is {}", name);
     return name;
@@ -285,7 +285,7 @@ private String getCanonicalHostname(String hostname) {
     return canonicalHostname;
   }
 
-  public CallbackHandler getUsernamePasswordHandler() {
+  private CallbackHandler getUsernamePasswordHandler() {
     if (username == null) {
       return null;
     }

client/src/test/java/org/asynchttpclient/spnego/SpnegoEngineTest.java

@@ -113,6 +113,44 @@ public void testSpnegoGenerateTokenWithCustomLoginConfig() throws Exception {
     Assert.assertTrue(token.startsWith("YII"));
   }
 
+  @Test
+  public void testGetCompleteServicePrincipalName() throws Exception {
+    {
+      SpnegoEngine spnegoEngine = new SpnegoEngine(null,
+          null,
+          "bob",
+          "service.ws.apache.org",
+          false,
+          null,
+          null,
+          null);
+      Assert.assertEquals("[email protected]", spnegoEngine.getCompleteServicePrincipalName("localhost"));
+    }
+    {
+      SpnegoEngine spnegoEngine = new SpnegoEngine(null,
+          null,
+          null,
+          "service.ws.apache.org",
+          true,
+          null,
+          null,
+          null);
+      Assert.assertNotEquals("HTTP@localhost", spnegoEngine.getCompleteServicePrincipalName("localhost"));
+      Assert.assertTrue(spnegoEngine.getCompleteServicePrincipalName("localhost").startsWith("HTTP@"));
+    }
+    {
+      SpnegoEngine spnegoEngine = new SpnegoEngine(null,
+          null,
+          null,
+          "service.ws.apache.org",
+          false,
+          null,
+          null,
+          null);
+      Assert.assertEquals("HTTP@localhost", spnegoEngine.getCompleteServicePrincipalName("localhost"));
+    }
+  }
+
   @AfterClass
   public static void cleanup() throws Exception {
     if (kerbyServer != null) {