After much faffing about, I have implemented the dynamic #OAuth2 client creation for #GoActivityPub services using the Client ID Metadata Document[1] that's been proposed as a replacement(?) for RFC7591 (Dynamic Client Registration Protocol).
For people interested in #ActivityPub #C2S (client to server), the #GoActivityPub services have gained the ability to dynamically register OAuth2 clients based on RFC7591.
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marius