issue on running rest API in controller

[sandeshpaudyal123]

@osiset
In Controller
I want to call metafields POST API on button click. The /updatemetafield route is hit and the code reaches the controller. On updatemetafield method in controller I run below code to get shop domain and password in order to create client and session but get the error "Attempt to read property "name" on null" ". Can any one help me to run the rest apis on controller.
Note: This way only works for first time when dashbaord is loading.

$shop_domain = Auth::user()->name;
$accesstoken = Auth::user()->password;