is KmsMasterKeyProvider shareable

Hi,

Have a look at the Javadoc: it states clearly that some methods are not thead safe.

See https://aws.github.io/aws-encryption-sdk-java/com/amazonaws/encryptionsdk/kms/KmsMasterKeyProvider.html#:~:text=Method%20Summary&text=This%20method%20is%20inherently%20not,the%20list%20of%20grant%20tokens.

This method is inherently not thread safe. Use withGrantTokens(List) or 
KmsMasterKey.setGrantTokens(List) instead. KmsMasterKeyProviders constructed using 
the builder will throw an exception on attempts to modify the list of grant tokens.

So, you should avoid this (deprecated) method to become thread safe.

Best,

Didier