This is one of many protocol behaviors described in ActivityPub.

Identifier

urn:uuid:4ddee17f-218e-4255-8e0a-edc1fe82f858

Content

Client to server... request MUST be authenticated with the credentials of the user to whom the outbox belongs

Origin

prefix Client to server interaction takes place through clients posting Activities to an actor's outbox. To do this, clients MUST discover the URL of the actor's outbox from their profile and then MUST make an HTTP POST request to this URL with the Content-Type of application/ld+json; profile="https://www.w3.org/ns/activitystreams". Servers MAY interpret a Content-Type or Accept header of application/activity+json as equivalent to application/ld+json; profile="https://www.w3.org/ns/activitystreams" for client-to-server interactions.

The request MUST be authenticated with the credentials of the user to whom the outbox belongs.
 
suffix The body of the POST request MUST contain a single Activity (which MAY contain embedded objects), or a single non-Activity object which will be wrapped in a Create activity by the server.

https://www.w3.org/TR/activitypub/

JSON

{
  "id": "urn:uuid:4ddee17f-218e-4255-8e0a-edc1fe82f858",
  "type": "Behavior",
  "uuid": "4ddee17f-218e-4255-8e0a-edc1fe82f858",
  "content": "Client to server... request MUST be authenticated with the credentials of the user to whom the outbox belongs\n",
  "context": [
    "https://www.w3.org/TR/activitypub/",
    {
      "name": "Client to server interaction"
    },
    {
      "name": "clients posting Activities to an actor's outbox"
    }
  ],
  "origin": {
    "source": "https://www.w3.org/TR/activitypub/",
    "section": {
      "id": "https://www.w3.org/TR/activitypub/#x6-client-to-server-interactions",
      "branch": [
        6
      ]
    },
    "selector": {
      "type": "TextQuoteSelector",
      "prefix": "Client to server interaction takes place through clients posting Activities to an actor's outbox. To do this, clients MUST discover the URL of the actor's outbox from their profile and then MUST make an HTTP POST request to this URL with the Content-Type of application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\". Servers MAY interpret a Content-Type or Accept header of application/activity+json as equivalent to application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\" for client-to-server interactions.\n",
      "exact": "The request MUST be authenticated with the credentials of the user to whom the outbox belongs.\n",
      "suffix": "The body of the POST request MUST contain a single Activity (which MAY contain embedded objects), or a single non-Activity object which will be wrapped in a Create activity by the server.\n"
    }
  },
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://socialweb.coop/ns/testing/context.json"
  ]
}