It would be a good UX improvement to allow keyAltName in the encryptedFieldsMap instead of always requiring {{keyId}}s, and reduce the effort to get started with CSFLE since it avoids the chicken-and-egg problem where users first need to create the keys using a half-autoencryption-configured MongoClient before being able to create the main MongoClient instance.

Since this work can probably be done entirely client-side, libmongocrypt seems like a good starting point.