Get a link token to start an OAuth or Cloud Link connection

First step of an OAuth flow: returns a short-lived token scoped to the member + provider. Pass the token to `GET /v1/devices/{slug}/oauth-url` (for the standard OAuth redirect flow) or to a hosted link UI (for Cloud Link).

curl -X POST "https://loading/v1/users/497f6eca-6276-4993-bfeb-53cbbbba6f08/devices/auth/token" \  -H "Content-Type: application/json" \  -d '{    "provider_slug": "string",    "redirect_uri": "string"  }'

{
  "data": {
    "token": "string",
    "expires_at": "2019-08-24T14:15:22Z"
  }
}

{
  "detail": [
    {
      "loc": [
        "string"
      ],
      "msg": "string",
      "type": "string"
    }
  ]
}