Your server proves who the customer is: identifier_hash is HMAC-SHA256 of identifier
with the HMAC token of the help centre's live chat inbox, made on your server. The session
is at the verified level, so sensitive requests (every complaint) open in full.
Authorization
Authorizationheaderrequired
The customer's portal session: the help centre's cookie, or the token from POST …/texa/verify or …/texa/identity as a bearer token.