Comprehensive and Detailed Step-by-Step Explanation:

A. Customer: Under the shared responsibility model, customers are responsible for securing their code and credentials in cloud environments.

B. Cloud service provider: Responsible for securing the underlying infrastructure, not customer-deployed applications or credentials.

C. Hacker: Exploited the breach but isn’t directly responsible for security lapses.

D. Code repository: Doesn’t inherently cause the issue unless mismanaged by the customer.