The spec now allows users to specify local.key as a byte array OR as the equivalent base64-encoded representation.

ORIGINAL DESCRIPTION

We now pass the KMS providers map as a BSON-encoded document to the libmongocrypt binary. The endpoint that accepts this map expects local.key to either be a base64-encoded string field or a BSON Binary field. Since there is no way to express a BSON binary value in Python 2 without importing bson.binary.Binary, as a workaround on Python 2 we instead encode the bytes as a base64 encoded string.

These changes were introduced in PYTHON-2371 (https://github.com/mongodb/libmongocrypt/pull/125)

We need to test this behavior.