Error with aws_base_encode for caching cmm

Hi, we're having issues with encrypting data locally with an IAM role for KMS access using caching_cmm.cpp with the error being thrown up as

Unexpected error in aws_base64_encode: Unknown Error Code

Just to be certain, we do not think its an IAM / permissions issue we are able to run string.cpp from the examples.

Start by reproducing the failure in caching_cmm.cpp using the local IAM/KMS setup described in the issue, then compare it with the working string.cpp example. Trace where the aws_base64_encode error is produced and determine why caching_cmm.cpp reports an unknown error. Done means the caching example encrypts successfully without that error.

Written by the indexing model from the issue text.