fix: Use provided national cloud as base URL and map it to the correct authentication endpoint

Author: Ndiritu

src/GraphServiceClient.php

@@ -44,9 +44,11 @@ public function __construct(
             parent::__construct($requestAdapter);
             return;
         }
-        parent::__construct(new GraphRequestAdapter(
+        $defaultRequestAdapter = new GraphRequestAdapter(
             new GraphPhpLeagueAuthenticationProvider($tokenRequestContext, $scopes, $nationalCloud)
-        ));
+        );
+        $defaultRequestAdapter->setBaseUrl("$nationalCloud/beta");
+        parent::__construct($defaultRequestAdapter);
     }
 
     /**

tests/GraphServiceClientTest.php

@@ -121,4 +121,10 @@ function (RequestInterface $request) {
         // cache is populated
         $this->assertInstanceOf(AccessToken::class, $customCache->getTokenWithContext($tokenRequestContext));
     }
+
+    public function testNationalCloudUsed(): void
++    {
++        $client = new GraphServiceClient(new ClientCredentialContext('tenant', 'client', 'secret'), [], NationalCloud::US_GOV);
++        $this->assertEquals(NationalCloud::US_GOV.'/beta', $client->getRequestAdapter()->getBaseUrl());
++    }
 }