The server's AWS KMS code assumes that any AWS KMS instance it needs to talk to is at kms.<region>.amazonaws.com. Some AWS KMS providers may be hosted at alternate domains.
For testing purposes, we support alternate URLs but we do not generate the signature correctly in these cases since our local mock kms does not validate the signature. The mock_kms server needs to updated to optionally verify the signature to ensure we have correctly implemented support for alternate kms. We can use local.10gen.cc or kms.local.10gen.cc as target hosts.
Python Auth Header Calculation: