Allow direct configuration of AWSCredentialsProvider

Summary: That way we can share the provider among different instances of RocksDB-Cloud

Test Plan: Compiles

Reviewers: hieu

Differential Revision: https://rockset.phacility.com/D10068

Author: igorcanadi

cloud/aws/aws_env.cc

@@ -115,6 +115,11 @@ Status AwsCloudAccessCredentials::GetCredentialsProvider(
     std::shared_ptr<Aws::Auth::AWSCredentialsProvider>* result) const {
   result->reset();
 
+  if (provider) {
+      *result = provider;
+      return Status::OK();
+  }
+
   AwsAccessType aws_type = GetAccessType();
   Status status = CheckCredentials(aws_type);
   if (status.ok()) {

include/rocksdb/cloud/cloud_env_options.h

@@ -81,6 +81,9 @@ class AwsCloudAccessCredentials {
   std::string secret_key;
   std::string config_file;
   AwsAccessType type{AwsAccessType::kUndefined};
+
+  // If non-nullptr, all of the above options are ignored.
+  std::shared_ptr<Aws::Auth::AWSCredentialsProvider> provider;
 };
 
 // Defines parameters required to connect to Kafka