docs: Update requirements

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1630 44740490-163a-0410-bde0-09ae8108e29a

docs/simplesamlphp-install.txt

@@ -25,11 +25,19 @@ This document is part of the simpleSAMLphp documentation suite.
 Prerequisites
 -------------
 
-PHP version >= 5.1.2. If you want to run the *Shibboleth 1.3* part of simpleSAMLphp, you must have PHP >= 5.2.
-
-Apache or some other webserver that allows you to run PHP.
-
-simpleSAMLphp is has been tested most thoroughly on different Linux versions, Unix, and Mac OS X. It also runs on Windows.
+ * Some webserver capable of executing PHP scripts.
+ * PHP version >= 5.2.0 if you are using simpleSAMLphp as an SP connected to a Shibboleth IdP; PHP version >= 5.1.2 if not.
+ * Suppoort for the following PHP extensions:
+   * Always required: `date`, `dom`, `hash`, `libxml`, `openssl`, `pcre`, `SPL`, `zlib`
+   * When encrypting assertions: `mcrypt`
+   * When authenticating against LDAP server: `ldap`
+   * When authenticating against RADIUS server: `radius`
+   * When saving session information to memcache-server: `memcache`
+   * When using database:
+     * Always: `PDO`
+     * Database driver: (`mysql`, `pgsql`, ...)
+
+What actual packages are required for the various extensions varies between different platforms and distributions.
 
 
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