authentication : Java Glossary

authentication

Ensuring that someone seeking to use some computer service is actually who they claim to be, or that the provider of the service is actually who it claims to be. Such schemes work with a shared secret such as a password or a private key. In some schemes, the actual secret need not be exchanged, just proof that other end knows the secret, e.g. by encrypting a random message with the private key. You can do web authentication with basic authentication where the browser brings up a dialog box for user name and password, form-based where the user fills in a form with username and password and perhaps other information, certificate based where the browser presents an X.509 certificate to the server to request access, and digest authorisation where the password is digested before being sent to the server to avoid it being snooped on.

Basic Scheme Authentication	Under the Hood
JDK 1.1-	Learning More
Digest Scheme Authentication	Links

Basic Scheme Authentication

when your Applet or JWS application tries to access something restricted on the server it gets a message back from the server telling it the realm (domain or subdomain) and the name of the password scheme the server wants to use, e.g. basic or digest. Your Applet then retries the request embedding the userid and password information in the requested way.

In Java 1.2+, in your client code, you can use the java.net.Authenticator class to handle the details. You extend the class overriding the getPasswordAuthentication method like this:

Then you then register your custom Authenticator with

import java.net.Authenticator;

//...

// hooking up your custom Authenticator
Authenticator.setDefault( new MyAuthenticator() );

You then do your GETs ignoring logons! Your Authenticator magically kicks in when needed and logs you in to the server. See the File I/O amanuensis or the CMP HTTP package for how. The technique reputedly works for HTTP and proxies. It may work for HTTPS. It even works for digest passwords. I don’t see how it could work for certificate style authentication, however, but who knows…

JDK 1.1-

If you are using an older Java, you will have to do it the Smith-Barney way (obscure reference to the late John Houseman):

Digest Scheme Authentication

For the more secure digest-style authentication, the protocol is more complex. It requires nine subfields. It is described in RFC 2617. Java Authenticator uses this method when the server specifies scheme= "digest". It works by sending an MD5 digest with each transaction, and changing the digest periodically. Your Applet does not need to get involved with the details of how it works. Authenticator handles it all transparently. You can fine tune how it works with networking properties:
http.auth.digest.validateServer=false
http.auth.digest.validateProxy=false
http.auth.digest.cnonceRepeat=5

Sun does not document which schemes Authenticator supports. It may support others besides basic, digest and ntlm. It does not work with cookies.

Under the Hood

You might wonder how after the login is complete that the server can tell if messages coming in from the Internet are from people who are already logged in. There are a number of ways of doing it. Some you might think would work don’t.

By IP. You might think the server could just check if an IP in a message header was from someone logged in. This does not work because IPs are shared. Everyone in your home on the LAN, when the access the Internet comes from the same IP, the IP of your router.
By TCP/IP session. You might think the server would just check that the message came in on the same TCP/IP session as the user logged in on. This won’t work since you often connect with multiple sessions, and you would not want to have to relogin just because a session tanked.
Basic. The server sends you id/password with every request that is restricted. This method is not secure since the id/password pair is in plain text for any snoop to see.
NTLM. This is a Microsoft proprietary protocol than will only work with Microsoft servers and clients. I don’t know how it works. Java supports it.
By Cookie. The server sends a cookie at login time, and the user includes this cookie with each message to the server. This method is not secure since anyone snooping can spoof the user by just copying the invariant cookie. Further, the client’s browser must be configured to accept cookies, a practice which invites all manner of malicious spying.
URL rewriting. The server sends unique URLs to different users. When they come back the server knows they could only have come from the client they were sent to.
By HTTP auth digest. RFC 2617 Here each incoming message is digitally signed in an unforgeable way. The disadvantage of this approach is it takes a bit more CPU time to compute the digests and requires the more transmission overhead. The advantage is it is the most secure method without resorting to a fully encrypted data stream.

Learning More

Sun’s Javadoc on Authenticator class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on PasswordAuthentication class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

	You can get the freshest copy of this page from:	or possibly from your local J: drive (Java virtual drive/mindprod.com website mirror)
	http://mindprod.com/jgloss/authentication.html	J:\mindprod\jgloss\authentication.html
	Please email your feedback for publication, errors, omissions, typos, formatting errors, ambiguities, unclear wording, broken/redirected link reports, suggestions to improve this page or comments to Roedy Green :
	Canadian Mind Products
	mindprod.com IP:[65.110.21.43]
view Blog	Your face IP:[38.107.191.105]
Feedback	You are visitor number 22,897.