Merge branch '6.4' into 7.0

* 6.4:
  [Security] Make `impersonation_path()` argument mandatory and add `impersonation_url()`

Author: fabpot

Impersonate/ImpersonateUrlGenerator.php

@@ -36,11 +36,20 @@ public function __construct(RequestStack $requestStack, FirewallMap $firewallMap
         $this->firewallMap = $firewallMap;
     }
 
-    public function generateImpersonationPath(string $identifier = null): string
+    public function generateImpersonationPath(string $identifier): string
     {
         return $this->buildPath(null, $identifier);
     }
 
+    public function generateImpersonationUrl(string $identifier): string
+    {
+        if (null === $request = $this->requestStack->getCurrentRequest()) {
+            return '';
+        }
+
+        return $request->getUriForPath($this->buildPath(null, $identifier));
+    }
+
     public function generateExitPath(string $targetUri = null): string
     {
         return $this->buildPath($targetUri);