Generally the Developer has little control over the setup of the Server and Network. Operations configures all of the network devices, the operating system, and even the Tomcat server. However, configuration problems can cause test failures, and the only way to fix these issues is to get the configuration fixed. Generally you only have to review this material when there is a major change to the network or server setup.
SAML Messages
The most important part of any Shibboleth login to an application occurs as it generates a "SAML Response" XML message and sends it to the Service Provider. The message contains a large amount of XML boiler plate and a very small amount of important content.
A lot of Shibboleth testing involves checking the SAML Response to make sure it has the right data for the Subject and for each supplied Attribute. This is determined by the configuration files for Shibboleth. It must find the EntityID of the Service Provider in a configured Metadata file, find the necessarily attributes released in the attribute-filter xml file, generate the SAML Response, and send it to the configured "ACS" URL in the Metadata. The Service Provider will accept the message if the EntityID and digital signature of the Shibboleth server match what it has been configured to expect.
However, Shibboleth passes data back to the Browser in response to something the Browser set to it, and the subsequent transmission of the Response from the Browser to the Service Provider is unrelated to the network configuration of the Shibboleth servers. There is almost nothing in this part of the transmission to configure or test.
IdP Initiated Login
An "IdP Initiated" test occurs when you click a URL that points to our Shibboleth server and provides the EntityID of one of our Service Provider partners:
http://localhost:8080/idp/profile/SAML2/Unsolicited/SSO?providerId=nobody.yale.edu
The hostname part ("localhost:8080") could reference a Sandbox test Shibboleth running on Tomcat on your desktop, or it could be a test version of Shibboleth running on a VM in the machine room where you have created an SSH tunnel connecting port 8080 on your desktop to the real Server port on the real Server VM.
At the end, after "providerId=" you add the EntityID of a partner. It is a Yale testing convention that the ID "nobody.yale.edu" is configured to release a very large number of attributes including most of the interesting ones you might want to check. It is the first test to make because is does so much it will point out most errors.
The Shibboleth code that processes an "Unsolicited/SSO" does not do any network validity checking. It doesn't care what the protocol (http or https), hostname, or port number are. However, during the processing it does Redirect the Browser to a different URL on the same Shibboleth server, and it order to do that it needs to figure out what its own URL actually is from the point of view of the Browser.
Shibboleth is running on some VM in the machine room. You could be accessing it through the public production URL ("https://auth.yale.edu/idp") but you could also have set up an SSH tunnel from your local computer port 8080 to the VM port 8080 (the port Tomcat uses). The problem is that Tomcat and Shibboleth cannot tell from the network protocol just how the network traffic is routed between the Browser and the VM. The only hint it has is the HTTP Host Header.
Initially the Browser will have generated a Host header based on the network address in the URL it started with. In these cases, the header will either be "http://localhost:8080" or else "https://auth.yale.edu". The Host header may pass through a number of intermediate devices, and some of them may edit some of the HTTP content, but the meaning of the Host header as "the network address of the server from the point of view of the Browser" should be preserved. Then when Shibboleth needs to Redirect the Browser from one of its URLs to another URL, it can use the Host header as the start of the Redirect URL and know that when the Browser can use it to get back to the same Shibboleth server.
If you submit an IdP Initiated Login to Shibboleth and immediately get a Browser redirect to a completely different URL location, then someone has messed up the Host header between the Browser and Shib.
There is a different Redirect problem when Shibboleth uses CAS to log you in. The convention with CAS is that Shib, like any other CAS client, provides a service= string that contains a URL in the Tomcat server to which CAS can Redirect the Browser after it has added the Service Ticket ID. For some reason, although the Unicon CAS-Shib itegration code has access to the Host header, it only uses that header to set the port number. The rest of the Service URL is constructed from a property that in the Yale Install Project is called "cas.target.url" and is supplied at install time.
The problem is that this property is not dynamic and it is not going to adjust between "localhost:8080" for an SSH tunnel and "auth.yale.edu" through the F5. Since it seems like a very bad practice to configure the VM with properties that will not work in production, if you discover that Shibboleth is Redirecting the Browser to CAS with a Service URL that cannot possibly get back to the Shib VM in the way you are currently accessing that VM, then you have to use one of the Client configuration tools described in the Client Configuration part of this set of documents to rewrite or reroute the Service URL (the Browser Redirector plugin can do it for example).
The IdP Initated Login provides the simplest set of tests. About 95% or more of Service Providers will accept IdP Initiated, and you should do all that testing first. It is also the simplest network setup because you only have to fix the two Redirect problems (Shib to Shib and CAS to Shib) if they happen to occur.
In fact, for initial testing it is not actually necessary for the SAML Response to be delivered to the Service Provider (or for it to be trusted if it does arrive there). If you are running the SAML Tracer in Firefox you can capture the SAML Response and usually determine if the Subject and Attributes are correct just by inspecting it.
However, for final 100% coverage testing, then you should use production credentials to generate a SAML Response the Service Provider will actually accept and log you on. Of course, for that to work the URL has to point to PREPROD Shibboleth, either directly through the F5 or through an SSH tunnel from localhost.
Change the EntityID at the end of the "Unsolicited/SSO" URL and you can verify that the right attributes are sent to any particular Service Provider.
SP Initiated
The IdP Initiated test was simplified because the code that handles the "Unsolicited/SSO" URL does not do any checks on the network address. Technically, the "Unsolicited/SSO" is a Shibboleth programming convention and not part of the SAML standard, so checks are not required.
However, if you go to the Service Provider and press a "Login from Yale" button or select Yale from a pulldown list of universities, then the SAML Request object generated by the Service Provider and the protocol by which it is sent to Shibboleth are part of the SAML standard, and that standard requires Shibboleth to do some extra checks that make the network configuration a bit more complicated.
Furthermore, while the network path from the Browser to the Service Provider (to send the Shibboleth Response) is just normal Yale networking and is not changed by the Shibboleth testing configuration, the SAML message that the SP sends to the Browser and then expects the Browser to deliver to Shib obviously is going to be affected by which Shib VM you want to use and how the Browser sends data to it.
Shibboleth processes the SAML Request first, before it even sends you to CAS in order to login. The Request has to go through a series of checks:
- The EntityID to which the Request is addressed has to match the EntityID configured to this Shibboleth server through the "idp.entityid" property on the Jenkins Install. In the IdP Initiated testing you can use any Shibboleth (PROD, TEST, DEV, or Sandbox) and the Response will be generated and traced so you can look at its contents. It is only when the Response finally gets to the SP that it will be rejected if it comes from the wrong Shibboleth. But with an SP Initiated login you have to send the Request to the Shibboleth selected by the SP or you don't even start to do any processing. Because SPs are almost always configured to talk only to PROD, that means the Shibboleth you send the Request to has to think it has the production Shibboleth EntityID (that is, it must have been installed with the "idp.entityID= https://auth.yale.edu/idp/shibboleth" property).
- The Service Provider will tell the Browser to send the Request (either by POSTing a form or by Redirect on a GET) to the SSO URL that the SP has in its copy of the Yale IdP Metadata. That will be a production URL, and so the Browser will be instructed to send the Request to "https://auth.yale.edu/idp/..." Since that will not be the actual URL of the test machine, you will have to use one of the tools described in the Client Configuration document to rewrite or reroute the request to the test VM.
- Shibboleth will validate the digital signature on the Request, but that will always work because the SP is genuine and is not itself being tested.
Now we get to the last test, which is harder and requires a longer description. The SAML protocol requires a Request to include the URL to which the Request is sent to also be data in an internal XML field of the Request, and it requires the IdP to check that this field is correct. Depending on whether the Request is sent as a POST or a Redirect, the URL for PROD Shib will be "https://auth.yale.edu/idp/profile/SAML2/POST/SSO" or "https://auth.yale.edu/idp/profile/SAML2/Redirect/SSO".
Of course, this URL will also have been included in the HTTP headers, and previously some mechanism was used to rewrite or reroute the HTTP flow to the test Shibboleth. That did not change the XML content. So now the problem is to ensure that the URL that the test Shibboleth server receives matches a URL that it reconstructs using the Host header and the HTTPServletRequest object it receives.
Of course, with open source you can download and read the Java code to see exactly how it is done. You can even find the Spring Bean statement that configures the comparison and replace it with new code that relaxes the rules. However, generally speaking if the Host header contains "https://auth.yale.edu" and Tomcat believes that the message arrived over SSL (at least as far as the proxy) then the comparison will work. So you will have a problem when you are trying to handle an SP Initiated Login and either:
- You use Redirector to rewrite the server URL before the Host header is generated instead of using the hosts file or Charles to reroute the request while preserving the "auth.yale.edu" hostname.
- You send the data over an SSH tunnel directly to non SSL port 8080 without any Proxy protocol or Tomcat configuration that says the data was originally SSL.
If the URL in the XML and the URL that Shibboleth generates don't match, Shibboleth writes an error message to the log containing the two strings it is comparing. You know you have to fix your client configuration when one of the two strings reported in the log contains:
- "http://localhost:8080/" - You have both problems, Redirector has rewritten the Host header and you have a tunnel to 8080.
- "http://auth.yale.edu" - The host header is right, but Tomcat doesn't think this is https.
- "https://auth.yale.edu:8080" - Tomcat knows this is https, but the host header had a port number inserted.
The Client Setup article will provide some configurations that are known to work. Others may also work, but you may take some time with trial and error trying to fix the last problems.
Background on Proxies and Tunnels
The first thing to say is that in almost no modern network is the hostname of the server that the Browser uses to get to Shibboleth ("auth.yale.edu") the actual name of the VM on which Shibboleth runs. In fact, it is almost never possible for the Browser to actually talk to Shibboleth directly. For security reasons, the network addresses and firewalls are set up to block outside access to server VMs, and a front end proxy machine provides the connection between the Browser and the Server. At Yale, that Proxy machine is called the F5.
Proxies have been part of HTTP since the early days of the World Wide Web. Originally they were used when the Internet was slow and it did not make sense for hundreds of computers at Yale to each independently download their own copies of widely used web pages. Today, you can put a proxy:
- On the same computer as the Browser. The Charles Web Debugging Proxy is a useful tool for testing.
- You can still find a client oriented proxy somewhere in the campus network, but this is no longer common or useful.
- The F5 sits between the secure environment of the servers in the machine room and the outside world of untrusted requesters.
- A front end (Nginx or Apache Web Server) can receive requests on ports 80 and 443 on the Shibboleth VM and they can forward those requests to Tomcat.
As a developer testing code, you probably only have control over the first type of Proxy, and if you chose to use it then we recommend Charles Web Debugging Proxy as the simplest tool.
However, if you run a test and the SAML Request send by the SP is being rejected because the generated string does not match the expected URL, then something is going wrong and it could be with any of the other intermediate devices or it could be a Tomcat configuration problem. So you have to understand something about how this stuff works in order to debug it.
The good news is that Tomcat fully expects that one or more proxies will exist between the Browser and the server VM, so it is quite flexible in its configuration. Shibboleth is not as flexible, but the fact that it can work at all means that if you get the proxies configured right then everything will be OK.
When the Browser generates any HTTP request, it creates a Host header. This header contains the protocol, hostname, and port number from the URL that the Browser is using to get to the application. For a request that thinks it is going to production Shibboleth, this is
Host: https://auth.yale.edu
This header can go through the network and the F5 unmodified, or it can be changed. There are other headers that proxies frequently generate to indicate processing they have done. There are standards and if you have a couple of days you might find and read through all of them.
However, there are two basic rules. First, if the Browser thinks it is talking to production Shibboleth, and the rerouting is done in the network configuration, then one solution is to leave the original Host header alone. On the other hand, if the Browser knows that the test Shibboleth is really at a different URL, then it might be a good idea to have something in the proxy path that changes the Host header so it has the auth.yale.edu value shown above. In other words, if you know it is right leave it alone, and if you know it is wrong, change it.
It is trivial for Operations to fix the header, but if they are not already doing it, this will be more trouble than it is worth. Configure the client to generate the right header in the first place.
If the header is right coming out of the client, and it is being set incorrectly in the proxy chain, then you have to get Operations to fix it.