Session ID: extend the regex to match possible hash representations

Improves #306
Relates to #335 & #336
Duplicated by #339

Issues:
 - PHP regenerates the session ID if it is not compliant
 - the regex checking the session ID does not cover all cases
   - different algorithms: md5, sha1, sha256, etc.
   - bit representations: 4, 5, 6

Fix:
 - `index.php`:
   - remove `uniqid()` usage
   - call `session_regenerate_id()` if an invalid cookie is detected
 - regex: support all possible characters - '[a-zA-Z,-]{2,128}'
 - tests: add coverage for all algorithms & bit representations

See:
 - http://php.net/manual/en/session.configuration.php#ini.session.hash-function
 - https://secure.php.net/manual/en/session.configuration.php#ini.session.hash-bits-per-character
 - http://php.net/manual/en/function.session-id.php
 - http://php.net/manual/en/function.session-regenerate-id.php
 - http://php.net/manual/en/function.hash-algos.php

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

1 files changed, 55 insertions, 0 deletions

diff --git a/tests/utils/ReferenceSessionIdHashes.php b/tests/utils/ReferenceSessionIdHashes.php
new file mode 100644
index 00000000..60b1c007
--- /dev/null
+++ b/tests/utils/ReferenceSessionIdHashes.php
@@ -0,0 +1,55 @@
+<?php
+/**
+ * Testing the untestable - Session ID generation
+ */
+class ReferenceSessionIdHashes
+{
+    // Session ID hashes
+    protected static $sidHashes = null;
+
+    /**
+     * Generates session ID hashes for all algorithms & bit representations
+     */
+    public static function genAllHashes()
+    {
+        foreach (hash_algos() as $algo) {
+            self::$sidHashes[$algo] = array();
+
+            foreach (array(4, 5, 6) as $bpc) {
+                self::$sidHashes[$algo][$bpc] = self::genSidHash($algo, $bpc);
+            }
+        }
+    }
+
+    /**
+     * Generates a session ID for a given hash algorithm and bit representation
+     *
+     * @param string $function           name of the hash function
+     * @param int    $bits_per_character representation type
+     *
+     * @return string the generated session ID
+     */
+    protected static function genSidHash($function, $bits_per_character)
+    {
+        if (session_id()) {
+            session_destroy();
+        }
+
+        ini_set('session.hash_function', $function);
+        ini_set('session.hash_bits_per_character', $bits_per_character);
+
+        session_start();
+        return session_id();
+    }
+
+    /**
+     * Returns the reference hash array
+     *
+     * @return array session IDs generated for all available algorithms and bit
+     *               representations
+     */
+    public static function getHashes()
+    {
+        return self::$sidHashes;
+    }
+}