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However, in 99% of real world cases most people have only the one production version of their application, and they cannot easily switch it back a forth between "auth.yale.edu" and "auth-test.yale.edu". Fortunately, you do not actually need to change the application and you do not need to change the network. You just need to change one browser on one test desktop computer.
Names and Addresses
Applications do not talk to Shibboleth directly. They send a URL to the Shibboleth server back to the client Web Browser, and the Web Browser talks to Shibboleth. When Shibboleth sends data back to the application, it digitally signs it to prove that it is authentic and has not been modified in route.
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Its all About the Browser
All applications that use Shibboleth know the URL of the Shibboleth server. However, they do not communicate directly over the network to Shibboleth. Instead, they send the URL of the Shibboleth server to the client Browser and tell the Browser to talk to Shibboleth and get a message addressed to the application containing information about the current logged in user. The Browser talks to the application, to Shibboleth, to CAS, and back to the application again. So while the application may know the name "auth.yale.edu" and Shibboleth may know the URL of the application, it is the Browser on the client desktop that translates that name into a network address of a particular computer that runs Shibboleth.
When a Browser goes to any "https://" URL, the server at the other end has to have a Certificate and key that proves that it is the server with the name the Browser expected to talk to. The Certificate and key of Yale servers are protected by ITS, but we can install the same files on two different network addresses as long as we control both of them and they do the same thing.
When Shibboleth is done, it generates a message specifically targeted to a particular application, and it digitally "signs" the message with a second Certificate and key that proves the message comes from "Production Shibboleth at Yale University". Again, these files are controlled by ITS and we can install them on a second machine.
The "auth.yale.edu" name is publicly associated with servers that are carefully controlled and change only after the changes are thoroughly tested. It may take weeks for a change to go all the way to Production, so to make testing possible there is a Pre-Production server that we can change in a matter of minutes that contains the same code, configuration, and Certificate/key files as Production. That server runs what we will be putting into production as soon as it is fully tested.
The Pre-Production server has its own name, but unfortunately the way that Shibboleth works, having a server with a different name is not useful. The application knows the URL for "auth.yale.edu" and tells the Browser to go to that name and no other.
So the problem is to reroute requests on the client desktop computer where the Browser is running, so that when any URL references "auth.yale.edu" the request goes to the Pre-Production Shibboleth and not to the regular Production machine.
Names and Addresses (the Hosts file)
Users reference servers by their name, but the actual communication uses a numeric "IP Address". A "Name Server" translates a name like "auth.yale.edu" to a particular IP address, and then the data is sent to that address. It is generally regarded as a bad practice to use IP addresses directly, because ITS staff reserves the right to move stuff around on campus and that may change the address. The name doesn't change.
Today (and this may change in the future) the IP address of Production Shibboleth is "130.132.35.36". You can verify this on your computer by using the command ". That address sends the Browser to our production Shibboleth VM.
However, every operating system since the beginning of the Internet has had an alternate way to resolve names locally using the "hosts" file. On Windows this is located at
nslookup auth.yale.edu" on Windows, Mac, or Linux computers.
Today (and this may change more quickly than the production address) the Pre-Production Shibboleth address is 128.36.64.90, and for this machine even the name may change. So the only place you will find this address is in this document. So before you do any testing, check back here to make sure the address has not changed.
There is a "hosts" file on every computer since the beginning of the Internet. On windows it is "c:\Windows\system32\drivers\etc\hosts" and on Mac and Unix Linux systems it is just " /etc/hosts". Every line in a hosts that file that begins with "#" is a comment and is ignored. Otherwise, a line in this file contains . On Windows the default supplied file is all comments, and in Mac/Linux the default file contains one or two lines. Each line has an IP address and one or more host names that are associated with this that address. Because the hosts This file is searched first , anything found there overrides the name lookup. So if you for every network name any of your applications talk to. Once you change the file, the new contents take effect immediately.
So the testing trick is to add one line to the hosts file in the formon the client desktop temporarily. The line reads:
128.36.64.90 auth.yale.edu
Then whenever a program (the Browser) looks for the name "auth.yale.edu" it goes to address "128.36.64.90" (the address of the pre-production VM for Shibboleth) instead of "130.132.35.36".
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