[security-dev 00727]: Re: Request for comment: How to enable credentials delegation in HTTP Negotiate?

[Max (Weijun) Wang]

On Mar 31, 2009, at 12:47 AM, Michael McMahon wrote:

> Max,
>
> One question. Would this mechanism work for any possible GSS  
> security mechanism?
> In other words, is all the information you need encapsulated inside  
> a single
> GSSCredential object?

Yes, this object is enough to perform a delegated GSSContext  
establishment. Of course, the requestGSSCredential() can also have the  
same arguments as in requestPasswordAuthentication() so that the user- 
provided method can take actions based on hostname etc.

>
> Also, java.net.Authenticator was designed very much for the original  
> HTTP authentication
> schemes (Basic and Digest) which is why it has all these methods for  
> getting
> the hostname, port, domain "prompt" string etc and NTLM more or less  
> fits in with
> this API as well.

Authenticator is also suitable for a normal Negotiate-scheme  
authentication, which asks for username and password and then uses  
JGSS-API to acquire a credential from the KDC server.

>
> So, this is a different way of doing it, where a pre-established  
> credential is used
> instead of a user being prompted to provide a username and password  
> based
> on the parameters supplied by the protocol.

Correct, in this case, this credential is received from another party  
(also thru JGSS-API) as a token, so there needs a new way to feed it  
into the HTTP client.

>
> At the very least, there would have to be a way to distinguish  
> between these two
> modes of operation. But I am wondering if a separate class might be  
> more appropriate
> (GSSAuthenticator). So, HttpURLConnection could check if a  
> GSSAuthenticator exists
> then it would probe that object for the credential. otherwise it  
> would fall back to
> the existing approach

Well, I think a username/password pair is also a kind of credential,  
so it's quite natural to use a single class to provide all of them.  
The fallback mechanism can be implemented in the class, if username/ 
password is needed, the requestPasswordAuthentication() method can be  
called.

An alternative design: How about not intrude the setDefault() method  
but make the GSSCredential itself a static field?

class Authenticator {

     private GSSCredential cred;

     public synchronized static GSSCredential  
setGSSCredential(GSSCredential c) {
         GSSCredential old = cred;
         cred = c;
         return old;
     }

     public static GSSCredential requestGSSCredential() {
         return cred;
     }
}

>
> One problem with extending Authenticator is that the plugin has a  
> fixed Authenticator
> implementation, that only handles usernames and passwords, and it  
> might not
> want to use this new mechanism.

I see. I wish the Authenticator was designed as cascade-able.



Thanks
Max

>
> - Michael
>
>
> Max (Weijun) Wang wrote:
>> Ping again, any suggestions?
>>
>> Thanks
>> Max
>>
>> On Nov 25, 2008, at 3:01 PM, Weijun Wang wrote:
>>
>>> Hi All
>>>
>>> The current implementation of HTTP Negotiate authentication has not
>>> enabled credential delegation (it simply acquires a new one using  
>>> either
>>> a cached TGT or username/password from Authenticator). This means  
>>> that
>>> in a multi-tier application, a middle tier cannot start an HTTP  
>>> request
>>> (to the backend server) on behalf of the client.
>>
>> Currently, java.net.Authenticator can only authenticate using a  
>> username/password pair, but cannot use an established credential.
>>
>>>
>>> I'm suggesting the following updates:
>>>
>>> 1. In java.net.Authenticator, add 2 methods
>>>
>>>   protected GSSCredential getGSSCredential() { // To be overrided
>>>       return null;
>>>   }
>>>   public static GSSCredential requestGSSCredential() {
>>>       Authenticator a = theAuthenticator;
>>>       if (a == null) {
>>>           return null;
>>>       } else {
>>>           return a.getGSSCredential();
>>>       }
>>>   }
>>>
>>> 2. In the implementation of the HTTP Negotiate auth scheme
>>> (sun.net.www.protocol.http.NegotiatorImpl),
>>>
>>>   GSSCredential deleg = Authenticator.requestGSSCredential();
>>>   context = manager.createContext(serverName,
>>>                                   oid,
>>>                                   deleg,   // this used to be null
>>>                                   GSSContext.DEFAULT_LIFETIME);
>>>
>>> Then, when an application developer is creating a GSS server that  
>>> wants
>>> to start an HTTP request using a delegated credential, she can  
>>> write:
>>>
>>>   // establish the GSSContext
>>>   final GSSCredential deleg = context.getDelegCred();
>>>   Authenticator.setDefault(new Authenticator() {
>>>           @Override
>>>           protected GSSCredential getGSSCredential() {
>>>               return deleg;
>>>           }
>>>   });
>>>   new URL("http://somewhere").openConnection().getInputStream();
>>>
>>> What's your comment?
>>>
>>> Thanks
>>> Max
>>>
>>
>