Implement a CloudFormation custom resource backed by an AWS Lambda function to generate a secure password string, then retrieve and apply this string using CloudFormation's Fn::GetAtt function for DB instance creation.

Utilize the AWS CodeBuild step in CodePipeline to execute the AWS CLI command 'aws secretsmanager get-random-password' to generate a secure password string, which is then passed as a CloudFormation parameter with NoEcho attribute for use in DB instance creation.

Develop a Lambda function for CloudFormation to create a secure password string, store it as a data field in the custom resource response, and use Fn::GetAtt to access it. Subsequently, create and reference this secret in AWS Secrets Manager for DB instance setup.

Leverage the AWS::SecretsManager::Secret CloudFormation resource to auto-generate a secure password, store it in AWS Secrets Manager, and dynamically reference this secret for the DB instance password during creation.