@pfefferle if you're satisfied with using a CLI tool, you can try the client I created for GoActivityPub based servers: https://git.sr.ht/~mariusor/box
It supports OAuth2 dynamic client creation either with CIMD or with RFC7591
It supports creating activities for publishing text content and some basic loading of information about ActivityPub objects.
In the near future it will also support proxyUrl to interact with secure fetch servers, but not just yet.
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