Add support for CSP nonces

CSP nonces are a feature available with CSP v2. Basically instead of saying "JS resources from the same domain are ok to be served" we now say "Ressources from everywhere are allowed as long as they add a `nonce` attribute to the script tag with the right nonce.

At the moment the nonce is basically just a `<?php p(base64_encode($_['requesttoken'])) ?>`, we have to decode the requesttoken since `:` is not an allowed value in the nonce. So if somebody does on their own include JS files (instead of using the `addScript` public API, they now must also include that attribute.)

IE does currently not implement CSP v2, thus there is a whitelist included that delivers the new CSP v2 policy to newer browsers. Check http://caniuse.com/#feat=contentsecuritypolicy2 for the current browser support list. An alternative approach would be to just add `'unsafe-inline'` as well as `'unsafe-inline'` is ignored by CSPv2 when a nonce is set. But this would make this security feature unusable at all in IE. Not worth it at the moment IMO.

Implementing this offers the following advantages:

1. **Security:** As we host resources from the same domain by design we don't have to worry about 'self' anymore being in the whitelist
2. **Performance:** We can move oc.js again to inline JS. This makes the loading way quicker as we don't have to load on every load of a new web page a blocking dynamically non-cached JavaScript file.

If you want to toy with CSP see also https://csp-evaluator.withgoogle.com/

Signed-off-by: Lukas Reschke <lukas@statuscode.ch>

2 files changed, 19 insertions, 4 deletions

diff --git a/lib/private/Security/CSRF/CsrfToken.php b/lib/private/Security/CSRF/CsrfToken.php
index bf61e339f77..dce9a83b727 100644
--- a/lib/private/Security/CSRF/CsrfToken.php
+++ b/lib/private/Security/CSRF/CsrfToken.php
@@ -33,6 +33,8 @@ namespace OC\Security\CSRF;
 class CsrfToken {
 	/** @var string */
 	private $value;
+	/** @var string */
+	private $encryptedValue = '';
 
 	/**
 	 * @param string $value Value of the token. Can be encrypted or not encrypted.
@@ -48,8 +50,12 @@ class CsrfToken {
 	 * @return string
 	 */
 	public function getEncryptedValue() {
-		$sharedSecret = base64_encode(random_bytes(strlen($this->value)));
-		return base64_encode($this->value ^ $sharedSecret) .':'.$sharedSecret;
+		if($this->encryptedValue === '') {
+			$sharedSecret = base64_encode(random_bytes(strlen($this->value)));
+			$this->encryptedValue = base64_encode($this->value ^ $sharedSecret) . ':' . $sharedSecret;
+		}
+
+		return $this->encryptedValue;
 	}
 
 	/**
diff --git a/lib/private/Security/CSRF/CsrfTokenManager.php b/lib/private/Security/CSRF/CsrfTokenManager.php
index d621cc2c29f..b43ca3d3679 100644
--- a/lib/private/Security/CSRF/CsrfTokenManager.php
+++ b/lib/private/Security/CSRF/CsrfTokenManager.php
@@ -34,6 +34,8 @@ class CsrfTokenManager {
 	private $tokenGenerator;
 	/** @var SessionStorage */
 	private $sessionStorage;
+	/** @var CsrfToken|null */
+	private $csrfToken = null;
 
 	/**
 	 * @param CsrfTokenGenerator $tokenGenerator
@@ -51,6 +53,10 @@ class CsrfTokenManager {
 	 * @return CsrfToken
 	 */
 	public function getToken() {
+		if(!is_null($this->csrfToken)) {
+			return $this->csrfToken;
+		}
+
 		if($this->sessionStorage->hasToken()) {
 			$value = $this->sessionStorage->getToken();
 		} else {
@@ -58,7 +64,8 @@ class CsrfTokenManager {
 			$this->sessionStorage->setToken($value);
 		}
 
-		return new CsrfToken($value);
+		$this->csrfToken = new CsrfToken($value);
+		return $this->csrfToken;
 	}
 
 	/**
@@ -69,13 +76,15 @@ class CsrfTokenManager {
 	public function refreshToken() {
 		$value = $this->tokenGenerator->generateToken();
 		$this->sessionStorage->setToken($value);
-		return new CsrfToken($value);
+		$this->csrfToken = new CsrfToken($value);
+		return $this->csrfToken;
 	}
 
 	/**
 	 * Remove the current token from the storage.
 	 */
 	public function removeToken() {
+		$this->csrfToken = null;
 		$this->sessionStorage->removeToken();
 	}