providers/proxy: fix nil error in claims

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

internal/outpost/proxyv2/application/mode_forward_nginx_test.go

@@ -70,7 +70,7 @@ func TestForwardHandleNginx_Single_Claims(t *testing.T) {
 	s, _ := a.sessions.Get(req, constants.SeesionName)
 	s.Values[constants.SessionClaims] = Claims{
 		Sub: "foo",
-		Proxy: ProxyClaims{
+		Proxy: &ProxyClaims{
 			UserAttributes: map[string]interface{}{
 				"username": "foo",
 				"password": "bar",