fix: correct credentials structure

Author: bilboque

src/Identity/v3/Api.php

@@ -695,10 +695,7 @@ public function postCredentials(): array
             'method' => 'POST',
             'path'   => 'credentials',
             'params' => [
-                'blob'      => $this->params->blob(),
-                'projectId' => $this->params->projectId(),
-                'type'      => $this->params->type('credential'),
-                'userId'    => $this->params->userId(),
+                'credential' => $this->params->credential(),
             ],
         ];
     }

src/Identity/v3/Params.php

@@ -333,4 +333,17 @@ public function blob(): array
             'description' => "This does something, but it's not explained in the docs (as of writing this)",
         ];
     }
+
+    public function credential(): array
+    {
+        return [
+            'type'       => 'object',
+            'properties' => [
+                'blob'      => $this->blob(),
+                'projectId' => $this->projectId(),
+                'type'      => $this->type('credential'),
+                'userId'    => $this->userId(),
+            ],
+        ];
+    }
 }