## Why is this an issue?

If the credentials provider is not specified when creating a new AwsClient with an AwsClientBuilder, the AWS SDK will execute some logic to identify it automatically.

While it will probably identify the correct one, this extra logic will slow down startup time, already known to be a hotspot.

You should therefore always define the logic to set the credentials provider yourself. This is typically done by retrieving it from the Lambda provided environment variable.

This will make the code more explicit and spare initialization time.

This rule reports an issue when the credentials provider is not set when creating an AwsClient.

### Noncompliant code example

    S3Client.builder()
        .region(Region.of(System.getenv(SdkSystemSetting.AWS_REGION.environmentVariable())))
        .build();

### Compliant solution

    S3Client.builder()
        .region(Region.of(System.getenv(SdkSystemSetting.AWS_REGION.environmentVariable()))
        .credentialsProvider(EnvironmentVariableCredentialsProvider.create())
        .build();

## Resources

- Tuning the AWS Java SDK 2.x to reduce startup time
- Optimizing cold start performance for AWS Lambda
- Environment variable configuration
- Default Credential Provider Chain