Kerberos with S4U2 extensions

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Kerberos with S4U2 extensions

Kishore Krishna M

  I am working on the below scenario:

Client1 interacts with Service1 which in turn interacts with Service 2. The
interaction with Service 2 should happen on behalf of Client1.
Authentication being used here is kerberos, and I have few issues in
explicitly setting the requestCredDelegation(true) on the client side. I
thought S4U2 self + S4U2 Proxy kerberos extensions could solve the issue.

These are the things I have done:

a) In the AD, On the Service1 account, enabled trusted delegation for
specific service.

b) In my Service1 java code, after the client <-> Server connection is
established: 1) I create the server credentials: serverCreds =
manager.createCredential(null, GSSCredential.DEFAULT_LIFETIME, krb5Oid,

2). Create the GSSName corresponding to the client GSSName other =
manager.createName(XXX, GSSName.NT_USER_NAME, krb5Oid);

3) GSSCredential clientcreds = ((ExtendedGSSCredential)

Impersonated client creds show up as:: [GSSCredential:
[hidden email] 1.2.840.113554.1.2.2
Initiate [class]
[hidden email] Initiate [class

4) Having the impersonated credential, I try to connect Service 1 to
Service 2, by creating the context :

GSSContext context = manager.createContext(serverName, krb5Oid,
impersonatedUserCredential, GSSContext.DEFAULT_LIFETIME); .......
context.initSecContext(token, 0, token.length);

I get an error of No Valid credentials found.
I have created a Subject from the impersonated Credentials and try to run a
privileged Action, but similar error shows up, no service ticket found in
the Subject.

I see that when a subject is created by passing in the Credentials,
Krb5ProxyCredential is being ignored,

"Skipped cred element:"

Could somebody let me know, why are the Krb5ProxyCredentials being ignored
when creating a subject and the proxied request fails with missing
credentials and no service ticket found.

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