Pseudonymization method that generates surrogates via
cryptographic hashing. Uses SHA-256.
The key size must be either 32 or 64 bytes.
Outputs a base64 encoded representation of the hashed output
(for example, L7k0BHmF1ha5U3NfGykjro4xWi1MPVQPjhMAZbSV9mM=).
Currently, only string and integer values can be hashed. See
https://cloud.google.com/sensitive-data-protection/docs/pseudonymization
to learn more.