Add username config to specify column.

Fix #15

Author: joselfonseca

config/config.php

@@ -30,5 +30,15 @@
     | the default location
     |
     */
-    'schema' => null
+    'schema' => null,
+    /*
+    |--------------------------------------------------------------------------
+    | Username Column
+    |--------------------------------------------------------------------------
+    |
+    | What column should be use for the username in the users table to find
+    | the user.
+    |
+    */
+    'username' => 'email'
 ];

src/GraphQL/Mutations/Login.php

@@ -19,7 +19,8 @@ public function resolve($rootValue, array $args, GraphQLContext $context = null,
     {
         $credentials = $this->buildCredentials($args);
         $response = $this->makeRequest($credentials);
-        $user = app(config('auth.providers.users.model'))->where('email', $args['data']['username'])->firstOrFail();
+        $model = app(config('auth.providers.users.model'));
+        $user = $model->where(config('lighthouse-graphql-passport.username'), $args['data']['username'])->firstOrFail();
         $response['user'] = $user;
         return $response;
     }