pcloud: fix initial config "Auth state doesn't match" message #4210

pCloud should be passing back the state parameter that rclone passed
in on config but it seems to have got lost somewhere.

This sets a work-around for the pCloud backend allowing an empty state
parameter.

See: https://forum.rclone.org/t/cannot-connect-to-pcloud/16592
See: https://forum.rclone.org/t/cannot-create-pcloud-config-file-on-osx/16583

backend/pcloud/pcloud.go

@@ -67,7 +67,10 @@ func init() {
 		Description: "Pcloud",
 		NewFs:       NewFs,
 		Config: func(name string, m configmap.Mapper) {
-			err := oauthutil.Config("pcloud", name, m, oauthConfig, nil)
+			opt := oauthutil.Options{
+				StateBlankOK: true, // pCloud seems to drop the state parameter now - see #4210
+			}
+			err := oauthutil.Config("pcloud", name, m, oauthConfig, &opt)
 			if err != nil {
 				log.Fatalf("Failed to configure token: %v", err)
 			}