Exchange Device Token

Exchange device token for session (primary deep link handler)

Request Parameters
POST https://read.lovelettersfromgod.com/auth/exchange

Long-lived device token

For device binding validation

To associate session with content

Expected Response
{
  "success": true,
  "session_id": "string",
  "user_id": "string",
  "letter_key": "string (optional)"
}