java - Accessing kerberos secured WebHDFS without SPnego

Question

I have a working application for managing HDFS using WebHDFS. I need to be able to do this on a Kerberos secured cluster.

The problem is, that there is no library or extension to negotiate the ticket for my app, I only have a basic HTTP client.

Would it be possible to create a Java service which would handle the ticket exchange and once it gets the Service ticket to just pass it to the app for use in a HTTP request? In other words, my app would ask the Java service to negotiate the tickets and it would return the Service ticket back to my app in a string or raw string and the app would just attach it to the HTTP request?

EDIT: Is there a similar elegant solution like @SamsonScharfrichter described for HTTPfs? (To my knowledge, it does not support delegation tokens)

EDIT2: Hi guys, I am still completly lost. Im trying to figure out the Hadoop-auth client without any luck. Could you please help me out again? I already spent hours reading upon it without luck. The examples say to do this:

* // establishing an initial connection
*
* URL url = new URL("http://foo:8080/bar");
* AuthenticatedURL.Token token = new AuthenticatedURL.Token();
* AuthenticatedURL aUrl = new AuthenticatedURL();
* HttpURLConnection conn = new AuthenticatedURL(url, token).openConnection();
* ....
* // use the 'conn' instance
* ....

Im lost already here. What initial connection do I need? How can

new AuthenticatedURL(url, token).openConnection();

take two parameters? there is no constructor for such a case. (im getting error because of this). Shouldnt a principal be somewhere specified? It is probably not going to be this easy.

    URL url = new URL("http://<host>:14000/webhdfs/v1/?op=liststatus");
    AuthenticatedURL.Token token = new AuthenticatedURL.Token();

    HttpURLConnection conn = new AuthenticatedURL(url, token).openConnection(url, token);

Answer 1

Using Java code plus the Hadoop Java API to open a Kerberized session, get the Delegation Token for the session, and pass that Token to the other app -- as suggested by @tellisnz -- has a drawback: the Java API requires quite a lot of dependencies (i.e. a lot of JARs, plus Hadoop native libraries). If you run you app on Windows, in particular, it will be a tough ride.

Another option is to use Java code plus WebHDFS to run a single SPNEGOed query and GET the Delegation Token, then pass it to the other app -- that option requires absolutely no Hadoop library on your server. The barebones version would be sthg like

URL urlGetToken = new URL("http://<host>:<port>/webhdfs/v1/?op=GETDELEGATIONTOKEN") ;
HttpURLConnection cnxGetToken =(HttpURLConnection) urlGetToken.openConnection() ;
BufferedReader httpMessage = new BufferedReader( new InputStreamReader(cnxGetToken.getInputStream()), 1024) ;
Pattern regexHasToken =Pattern.compile("urlString[": ]+(.[^" ]+)") ;
String httpMessageLine ;
while ( (httpMessageLine =httpMessage.readLine()) != null)
{ Matcher regexToken =regexHasToken.matcher(httpMessageLine) ;
  if (regexToken.find())
  { System.out.println("Use that template: http://<Host>:<Port>/webhdfs/v1%AbsPath%?delegation=" +regexToken.group(1) +"&op=...") ; }
}
httpMessage.close() ;

That's what I use to access HDFS from a Windows Powershell script (or even an Excel macro). Caveat: with Windows you have to create your Kerberos TGT on the fly, by passing to the JVM a JAAS config pointing to the appropriate keytab file. But that caveat also applies to the Java API, anyway.