If you are using Asana to manage client work, there is a good chance you’ll need to ask for the client's approval at one point. You could use email, of course, but that would not be as fun as using Asana, right?
The solution kinda depends on the situation. Do you need a one-time approval from a client you will never see again, and then need a “temporary” solution? Or do you need regular approval from the same clients, and thus need a more “permanent“ solution?
The permanent and most straightforward solution would be to add the client as a guest of a special project called “Approval”. You can then multi-home the tasks you need approval for inside this project. Quick reminder: multi-homing means having a single task into several projects. The Approval project would need to have the proper custom fields, probably something like an approval status field (with values like “To Approve”, “Approved”, “Rejected”). This solution has a major limitation: you need the client to agree on using Asana. The solution also has a couple of setup steps: you need to make sure the client is notified when a new task is added to their project (using the member permission and notification settings). You also need to make sure the tasks you share with the client doesn’t contain any sensitive information. If you are not able to share the actual task, you’ll need a workaround, sharing another task linked to the first one.
The temporary solution could be to host the things to approve (a document, an image) on a dedicated online storage solution, and name it accordingly. You can then have an “Approval and client requests” project, attached to a Form containing questions like “Date, Document name, Feedback, Requests”. Then you can share a link to this form with your client, using your regular tool (Slack, Whatsapp, email). When the client fills the form, you get a nice Asana task you can treat, pass around and archive.
As a manager: make sure to test the solution you choose, first within your team, acting as guests with their personal email address for example, and then with the client you are most comfortable with. Don’t expect the client to follow the rules: they will complete tasks when you said to only change the status, or will only change the assignee without changing the status. It will take time to train everyone, but it is worth it!