You could save yourself some hassle and make urls and IDs the same value. But you do you 
R
rimu@piefed.social
@rimu@piefed.social
Posts
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Recommend object URL should 301 to AP resource -
Recommend object URL should 301 to AP resourceObject IDs should really be retrievable by http GET. See section 3.2 of https://www.w3.org/TR/activitypub