minor #6234 File System Security Issue in Custom Auth Article (finished) (mattjanssen, WouterJ)

This PR was merged into the 2.3 branch.

Discussion
----------

File System Security Issue in Custom Auth Article (finished)

Finishes #5846

Original description:

 > | Q             | A
 > | ------------- | ---
 > | Doc fix?      | yes
 > | New docs?     | no
 > | Applies to    | all
 > | Fixed tickets | #5845
 >
 > I hope to address this security concern: If `$token->nonce` is set to [ANY USER INPUT] and later we run `file_put_contents($token->nonce, time())` are we allowing hackers to destroy any www-writable file in the system?
 >
 > I did notice that `$nonce` is run through `base64_decode($nonce)` later in the article, implying nonce needs to be a Base64 string. Could this Regex be updated to only accept a Base64 string `[a-zA-Z+/]+={0,2}` for the nonce?
 >
 > At the same time, Base64 allows `/` characters, so `file_put_contents()` would fail in those cases, so even this change, while secure, seems flawed. Replace [+/] with [-_]?

Commits
-------

673fd71 Hash nonce when using as file name
5f125f3 File System Security Issue in Custom Auth Article

Author: xabbuh

cookbook/security/custom_authentication_provider.rst

@@ -130,7 +130,7 @@ set an authenticated token in the security context if successful.
         {
             $request = $event->getRequest();
 
-            $wsseRegex = '/UsernameToken Username="([^"]+)", PasswordDigest="([^"]+)", Nonce="([^"]+)", Created="([^"]+)"/';
+            $wsseRegex = '/UsernameToken Username="([^"]+)", PasswordDigest="([^"]+)", Nonce="([a-zA-Z0-9+/]+={0,2})", Created="([^"]+)"/';
             if (!$request->headers->has('x-wsse') || 1 !== preg_match($wsseRegex, $request->headers->get('x-wsse'), $matches)) {
                 return;
             }
@@ -256,14 +256,17 @@ the ``PasswordDigest`` header value matches with the user's password.
 
             // Validate that the nonce is *not* used in the last 5 minutes
             // if it has, this could be a replay attack
-            if (file_exists($this->cacheDir.'/'.$nonce) && file_get_contents($this->cacheDir.'/'.$nonce) + 300 > time()) {
+            if (
+                file_exists($this->cacheDir.'/'.md5($nonce))
+                && file_get_contents($this->cacheDir.'/'.md5($nonce)) + 300 > time()
+            ) {
                 throw new NonceExpiredException('Previously used nonce detected');
             }
             // If cache directory does not exist we create it
             if (!is_dir($this->cacheDir)) {
                 mkdir($this->cacheDir, 0777, true);
             }
-            file_put_contents($this->cacheDir.'/'.$nonce, time());
+            file_put_contents($this->cacheDir.'/'.md5($nonce), time());
 
             // Validate Secret
             $expected = base64_encode(sha1(base64_decode($nonce).$created.$secret, true));