I'm allowing users to submit posts from the frontend. Some of these posts may have been written someone else first, so we need to allow them to enter the canonical URL. I have All-in-one SEO installed which provides a way to update the canonical URL for each post in wp-admin, so I'm figuring out how I can create a metabox field to show on the frontend submission and have it update the canonical URL field.
If the canonical URL field of All-in-one SEO saved value to the database as a custom field, then you can use the form hook to update the field value by using the WordPress function update_post_meta().
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