AZ702: Who is signed in was changed

Who is signed in is signed by authz.act_as() for the transaction. Setting authz.user_id (or the other authz.* settings) directly, or changing them after signing in, isn't believed: the app role can't choose its own user. Sign in with authz.act_as(), authz.login_key() or authz.login_jwt() instead.

Reported to the app, by the authz.* functions and the policy's rules: the code is in the error's HINT (rowfence help AZ709), and the SDKs' errors carry it as code.