Support configuration of KMS provider credentials with a Supplier

[jyemin]

JAVA-4504

[rozza]

It seems redundant to have and use both:

    private final Map<String, Map<String, Object>> kmsProviders;
    private final Map<String, Supplier<Map<String, Object>>> kmsProviderSupplierMap;

Should the maps be merged by the builder? - It may make it easier to debug if users have the same key in both settings (eg a warning could be logged).

This way internally only getKmsProviderSupplierMap is used? and getKmsProviders() could be deprecated. The builder could keep both setters for simplicity as translating a value to a supplier of a value is trivial.

[jyemin]

Should the maps be merged by the builder?

It's actually required to have the same key in both maps. The kmsProviders map is for when you know the credentials up front and they don't need to be refreshed for the lifetime of the MongoClient. The kmsProviderSupplierMap is for when you don't know the credentials up front and/or they need to be refreshed periodically. But if you need to use the latter, it's still required that you have an empty map in the former, e.g. map.put("aws", Collections.emptyMap()), just to indicate that you want to use "aws" at all.

[kevinAlbs]

LGTM. MONGOCRYPT-394 is in review. I do not think it impacts the changes in this PR.

[stIncMale]

I found that both the method name and the documentation is confusing because of the provider/supplier word play (the same is applicable to the corresponding setter and to the counterpart in the ClientEncryptionSettings class). The problem is further aggravated by the method getKmsProviders, for which getKmsProviderProperties appears to be a more appropriate name, or better just getKmsProperties (we can't change it). In order to mitigate the problem I propose the following:

• Rename the method to getKmsProviderPropertySuppliers or getKmsPropertySuppliers. We don't have the "Map" suffix in the getKmsProviders method, and it does not seem helpful here because a user may see it's a Map from the explicit return type. Having "Properties" part in the name is inconsistent with the name of the method getKmsProviders, but is helpful as it separates the "Provider" and "Supplier" parts.
• Rename the kmsProviderSupplierMap field/parameter accordingly in this class and in MongoCryptHelper, Crypt.
• Never use just "provider" in the documentation of the method, use "KMS provider" instead.
• Never use just "Supplier" or "supplier" in the documentation of the method, use "Supplier of properties" instead.

Example:

  /**
     * This method is similar to {@link #getKmsProviders()},
     * but instead of getting properties for KMS providers,
     * it gets {@link Supplier}s of properties.
     * <p>If {@link #getKmsProviders()} returns empty properties for a KMS provider,
     * the driver will use a {@link Supplier} of properties configured for the KMS provider
     * to obtain a non-empty properties.</p>
     *
     * @return A {@link Map} where keys identify KMS providers,
     * and values specify {@link Supplier}s of properties for the KMS providers.
     * @see #getKmsProviders()
     * @since 4.6
     */

[jyemin]

I went with kmsProviderPropertySuppliers as the property name. PTAL

I haven't touched the Javadoc yet.

[jyemin]

For Javadoc changes, it would be easier if you propose the changes directly by adding a commit.

[stIncMale]

The proposed Java API documentation changes: stIncMale@57f5aac.

[jyemin]

Reviewed and pushed

[stIncMale]

.