A base64 encoded DER representation of a private key, which is shared between devices for a single app.
The siteID needs to be an unsigned 64 bit integer > 0, i.e. either a
regular non-fractional number or a BigInt in the range between 1
and 2^64 - 1 (inclusive).
An identity with intermediate level of security where all users and devices are trusted and a single shared secret (key) between all peers satisfies the security requirements.
NOTE: This identity type is only supported for Node environments, using this to create a Ditto instance in the web browser will throw an exception.