the connector schemas are shared between authn, auth and bridges,
the difference is that authn and authz configs are unions like:
[
{mongo_type = rs,
...
}
{another backend config}
]
however the brdige types are maps like, for example:
mongodb_rs.$name {
mongo_type = rs
...
}
in which case, the mongo_type is not required.
in order to keep the schema static as much as possible,
this field is chanegd to 'required => false' with a default value.
However, for authn and authz, the union selector will still raise
exception if the there is no type provided.
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