Shibboleth SP documentation (#80)

Documentation on a solution for Shibboleth SP.
This solution is in production for Stockholm University, and therefor validated working.

doc/auth-shibboleth-sso.md

@@ -0,0 +1,60 @@
+# Shibboleth SP Implementation
+
+This is a short documentation on how you can setup wg-ui with Shibboleth SP (and apache)
+as auth proxy
+
+The documentation will not cover how to configure `shibd` or the IdP part of this integration.
+The [upstream documentation](https://wiki.shibboleth.net/confluence/) or
+[SWAMIDs
+documentation](https://wiki.sunet.se/display/SWAMID/SAML+WebSSO+Service+Provider+Best+Current+Practice)
+could point you in the right direction.
+
+## SSO Proxy & Auth
+
+This example uses
+[eduPersonPrincipalName](https://www.internet2.edu/media/medialibrary/2013/09/04/internet2-mace-dir-eduperson-201203.html#eduPersonPrincipalName)
+(or eppn as Shibboleth calls it) as the  primary key to identify users. Make
+sure that it is released from the IdP to the SP as a SAML attribute. The
+attributes(s) are then forward/proxied as request header to the application.
+
+The only thing that needs to be configured in the Wireguard UI end is that the
+application needs to be started with the `--auth-user-header` flag set to
+`eppn`.
+
+### The `apache` configuration
+
+```
+<VirtualHost *:443>
+    <LocationMatch "/">
+        AuthType Shibboleth
+        Require shib-attr entitlement ~ ^urn:mace:swami.se:gmai:vpn:user$
+        ShibRequireSessionWith idp.example.com
+        ShibUseHeaders On
+    </LocationMatch>
+
+    SSLCertificateFile    /path/to/vpn.example.com.pem
+    SSLCertificateKeyFile /path/to/vpn.example.com.key
+    SSLCertificateChainFile /path/to/CA.crt
+
+    ProxyPass "/" "http://127.0.0.1:8080/"
+    ProxyPassReverse "/" "http://127.0.0.1:8080/"
+</VirtualHost>
+```
+
+#### Configuration in depth
+
+```
+Require shib-attr entitlement ~ ^urn:mace:swami.se:gmai:su-vpn:user$
+```
+By default apache and shibd lets everyone through and since Wireguard UI has no
+knowlege about the user in beforehand we release another
+([eduPersonEntitlement](https://www.internet2.edu/media/medialibrary/2013/09/04/internet2-mace-dir-eduperson-201203.html#eduPersonEntitlement) (or entitlement as Shibboleth calls it))
+from the IdP to the SP and require a specific value on the user in order to be
+allowed to use the service.
+
+```
+ShibUseHeaders On
+```
+
+This enables `shibd` to publish SAML attributes to the application (in this case
+proxy) through request headers.