authentication : Java Glossary

Basic Scheme Authentication

InJava version 1.2 or later, 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 into the server. See the File I/O amanuensis or the CMP HTTP package for how. The technique reputedly works for HTTP (Hypertext Transfer Protocol) and proxies. It may work for HTTPS (Hypertext Transfer Protocol over SSL (Secure Socket Layer)). It even works for digest passwords. I don’t see how it could work for certificate style authentication, however, but who knows…

Java version 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 does not have a method to tell you which schemes Authenticator supports or what the official scheme names are. It may support others besides basic, digest, ntlm and spnego (Kerberos). It does not work with cookies or forms.

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.

1. By IP (Internet Protocol). 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 (Local Area Network), when the access the Internet comes from the same IP, the IP of your router.
2. By TCP/IP (Transmission Control Protocol/Internet Protocol) 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.
3. 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.
4. NTLM (New Technology LAN Manager protocol). 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.
5. 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.
6. URL (Uniform Resource Locator) 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.
7. 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 (Central Processing Unit) 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.

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