8044215: Unable to initiate SpNego using a S4U2Proxy GSSCredential (Krb5ProxyCredential)

Reviewed-by: mullan

src/share/classes/sun/security/jgss/krb5/Krb5Context.java

@@ -241,8 +241,11 @@ class Krb5Context implements GSSContextSpi {
      * establishment.
      */
     public final void requestCredDeleg(boolean value) throws GSSException {
-        if (state == STATE_NEW && isInitiator())
-            credDelegState  = value;
+        if (state == STATE_NEW && isInitiator()) {
+            if (myCred == null || !(myCred instanceof Krb5ProxyCredential)) {
+                credDelegState  = value;
+            }
+        }
     }
 
     /**

test/sun/security/krb5/auto/S4U2proxy.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 6355584
+ * @bug 6355584 8044215
  * @summary Introduce constrained Kerberos delegation
  * @compile -XDignore.symbol.file S4U2proxy.java
  * @run main/othervm S4U2proxy krb5
@@ -69,6 +69,10 @@ public class S4U2proxy {
         Context p = s.delegated();
 
         p.startAsClient(OneKDC.BACKEND, mech);
+
+        // 8044215: requestCredDeleg is useless and harmless
+        p.x().requestCredDeleg(true);
+
         b.startAsServer(mech);
         Context.handshake(p, b);