Refactor common code for getting the signature key.

src/GaryJones/OAuth/HmacSha1.php

@@ -55,15 +55,7 @@ class HmacSha1 extends SignatureMethod
     public function buildSignature(Request $request, Client $client, Token $token = null)
     {
         $base_string = $request->getSignatureBaseString();
-        $request->base_string = $base_string;
+        $key = $this->getSignatureKey($client, $token);
-
-        $key_parts = array(
-            $client->getSecret(),
-            ($token) ? $token->getSecret() : ''
-        );
-
-        $key_parts = Util::urlencodeRfc3986($key_parts);
-        $key = implode('&', $key_parts);
 
         return base64_encode(hash_hmac('sha1', $base_string, $key, true));
     }

src/GaryJones/OAuth/PlainText.php

@@ -52,15 +52,6 @@ class PlainText extends SignatureMethod
      */
     public function buildSignature(Request $request, Client $client, Token $token = null)
     {
-        $key_parts = array(
+        return $this->getSignatureKey($client, $token);
-            $client->getSecret(),
-            ($token) ? $token->getSecret() : ''
-        );
-
-        $key_parts = Util::urlencodeRfc3986($key_parts);
-        $key = implode('&', $key_parts);
-        $request->base_string = $key;
-
-        return $key;
     }
 }

src/GaryJones/OAuth/SignatureMethod.php

@@ -44,6 +44,25 @@ abstract class SignatureMethod
      */
     abstract public function buildSignature(Request $request, Client $client, Token $token = null);
 
+    /**
+     * Get the signature key, made up of client and optionally token shared secrets.
+     *
+     * @param GaryJones\OAuth\Client  $client
+     * @param GaryJones\OAuth\Token   $token
+     *
+     * @return string
+     */
+    public function getSignatureKey(Client $client, Token $token = null)
+    {
+        $key_parts = array(
+            $client->getSecret(),
+            ($token) ? $token->getSecret() : '',
+        );
+
+        $key_parts = Util::urlencodeRfc3986($key_parts);
+        return implode('&', $key_parts);
+    }
+
     /**
      * Verifies that a given signature is correct.
      *