The wire contract

Affordant works against one simple convention: the server enriches each resource with _self and _actions. Each action is { href, method, accepts? }, and the presence of a rel encodes permission.

The envelope

// GET /orders/8f3a2c — anonymous caller
{
  "id": "8f3a2c",
  "total": 4200,
  "status": "shipped",
  "_self":    { "href": "/orders/8f3a2c", "method": "GET" },
  "_actions": {
    "track": { "href": "/orders/8f3a2c/tracking", "method": "GET" }
  }
}

// same request, the order's owner → one more affordance
  "_actions": {
    "track":  { "href": "...", "method": "GET" },
    "cancel": { "href": "/orders/8f3a2c/cancel", "method": "POST" }
  }

The owner gets a cancel link; everyone else simply doesn't. The frontend renders the cancel button off the presence of that link — it never re-derives "can this user cancel?".

The shape, typed

type HateoasMethod = 'GET' | 'POST' | 'PUT' | 'PATCH' | 'DELETE'

interface HateoasAction {
  href: string
  method: HateoasMethod
  accepts?: string // request media type; defaults to application/json
}

type HateoasResource<T> = T & {
  _self?: HateoasAction
  _actions: Record<string, HateoasAction>
}

• href — where the action lives. It comes from the server's router, never hardcoded in the client.
• method — the HTTP verb to use. The client doesn't guess it.
• accepts — the media type the action expects in the request body. When omitted, Affordant sends application/json.

Why presence-as-permission matters

A rel is absent whenever the action is not available to this caller right now:

• not authorized (wrong role, not the owner),
• wrong state (the order already shipped, the draft is already published),
• feature off (flag disabled, plan doesn't include it).

The client doesn't need to know which of those reasons applies. It asks can(order, 'cancel') and trusts the answer. All of that branching logic stays on the server, where the authoritative state lives — and changing it never requires a frontend deploy.

This is Richardson Maturity Model Level 3, seen from the consumer's side: the client is driven by the controls the server hands it.