In mongodb/libmongocrypt@90cb575 for
MONGOCRYPT-272 (released in libmongocrypt 1.1.0), _mongocrypt_parse_required_binary was changed to accept a base64-encoded UTF-8 string instead of just a BSON binary type.
This was relevant to the new GCP integration, but I believe it also affects parsing of "local.key" for KMS provider configurations. Should this be discussed in the docs for mongoc_auto_encryption_opts_set_kms_providers?
According to mongodb/mongo-c-driver#695 (comment), the integration of GCP in
CDRIVER-3799 was the first time that libmongoc started to rely on libmongocrypt to parse options directly. As such, this likely only affects 1.18+ versions of libmongoc.