aws c++ sdk authentication problem

When you're experiencing authentication issues with the AWS SDK for C++, there are several things to check:

1. First, ensure your credentials are properly set up. The AWS SDK for C++ uses the DefaultAWSCredentialsProviderChain, which looks for credentials in the following order:

• Environment variables (AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY)
• AWS credentials file (~/.aws/credentials on Linux/Mac or %USERPROFILE%.aws\credentials on Windows)
• IAM role for Amazon EC2 (if running on EC2)

2. Verify that your credentials file is correctly formatted. After running "aws configure", it should have created a file with a structure like:

[default]
aws_access_key_id = YOUR_ACCESS_KEY
aws_secret_access_key = YOUR_SECRET_KEY
region = YOUR_REGION

3. Check if your credentials have the necessary permissions. Even though you've downloaded credentials, the IAM user might not have the required permissions to access S3 services.

4. You can test if your credentials are working with the AWS CLI by running:

aws sts get-caller-identity

This will show you which identity you're authenticated as.

5. If you're using temporary credentials, they might have expired. Temporary credentials include an additional session token and have a limited lifetime.

6. If you're running your application in a specific region, make sure to set the region in your client configuration:

clientConfig.region = "your-region";

The hello_s3.cpp example you're using actually includes a helpful check that explicitly tests authentication before attempting to list buckets, which is why you're seeing the "Failed authentication" message rather than just getting zero buckets returned.
Sources
Authenticate AWS credentials without secret key and access key using AWS SDK for Java | AWS re:Post
Can we provide temporary access key,ID and session token in AWS Credentials File | AWS re:Post
Amazon S3 examples using SDK for C++ - AWS SDK Code Examples
AWS was not able to validate the provided access credentials | AWS re:Post