fs: change Config callback into state based callback #3455

This is a very large change which turns the post Config function in
backends into a state based call and response system so that
alternative user interfaces can be added.

The existing config logic has been converted, but it is quite
complicated and folloup commits will likely be needed to fix it!

Follow up commits will add a command line and API based way of using
this configuration system.

fs/config/authorize.go

@@ -11,12 +11,14 @@ import (
 
 // Authorize is for remote authorization of headless machines.
 //
-// It expects 1 or 3 arguments
+// It expects 1, 2 or 3 arguments
 //
 //   rclone authorize "fs name"
+//   rclone authorize "fs name" "base64 encoded JSON blob"
 //   rclone authorize "fs name" "client id" "client secret"
 func Authorize(ctx context.Context, args []string, noAutoBrowser bool) error {
 	ctx = suppressConfirm(ctx)
+	ctx = fs.ConfigOAuthOnly(ctx)
 	switch len(args) {
 	case 1, 2, 3:
 	default:
@@ -60,7 +62,7 @@ func Authorize(ctx context.Context, args []string, noAutoBrowser bool) error {
 	m.AddSetter(outM)
 	m.AddGetter(outM, configmap.PriorityNormal)
 
-	err = ri.Config(ctx, name, m)
+	err = PostConfig(ctx, name, m, ri)
 	if err != nil {
 		return err
 	}