Explanation
Contracts and SLAs are legal documents that define the roles, responsibilities, expectations, and obligations of both the cloud service provider (CSP) and the cloud customer. They also specify the terms and conditions for service delivery, performance, availability, security, compliance, data protection, incident response, dispute resolution, liability, and termination. An auditor should review these documents to assess the alignment of the CSP's services with the customer's business requirements and risk appetite, as well as to identify any gaps or inconsistencies that may pose legal risks. References:
ISACA, Certificate of Cloud Auditing Knowledge (CCAK) Study Guide, 2021, p. 35-36 Cloud Security Alliance (CSA), Cloud Controls Matrix (CCM) v4.0, 2021, GRM-01: Contracts and SLAs

The optimal and most efficient mechanism to assess the controls that the provider is responsible for is to review third-party audit reports. Third-party audit reports are independent and objective assessments of the provider's security, compliance, and performance, conducted by qualified and reputable auditors. Third-party audit reports can provide assurance and evidence that the provider meets the industry standards and best practices, as well as the contractual and legal obligations with the SaaS company. Third-party audit reports can also cover a wide range of controls, such as data security, encryption, identity and access management, incident response, disaster recovery, and service level agreements. Some examples of third-party audit reports are ISO 27001 certification, SOC 1/2/3 reports, CSA STAR certification, and FedRAMP authorization123.
Reviewing the provider's published questionnaires (A) may not be optimal or efficient, as the published questionnaires may not be comprehensive or up-to-date, and may not reflect the actual state of the provider's controls. The published questionnaires may also be biased or inaccurate, as they are produced by the provider themselves.
Directly auditing the provider may not be feasible or necessary, as the independent contractor may not have access to the provider's environment or data, and may not have the authority or expertise to conduct such an audit. The independent contractor should rely on the third-party audit reports and certifications to assess the provider's compliance with relevant standards and regulations.
Sending a supplier questionnaire to the provider (D) may not be optimal or efficient, as the supplier questionnaire may not cover all the aspects of the provider's controls, and may not provide sufficient evidence or assurance of the provider's security maturity. The supplier questionnaire may also take a long time to complete and verify, and may not be consistent with the industry standards and best practices. References :=
* How to Evaluate Cloud Service Provider Security (Checklist)
* Cloud service review process - Cloud Adoption Framework
* How to choose a cloud service provider | Microsoft Azure

ISO/IEC 27017:2015 is a standard that provides guidelines for information security controls applicable to the provision and use of cloud services by providing additional implementation guidance for relevant controls specified in ISO/IEC 27002, as well as additional controls with implementation guidance that specifically relate to cloud services1. ISO/IEC 27017:2015 is designed to be used by organizations for cloud services that intend to select controls within the process of implementing an information security management system based on ISO/IEC 270011. ISO/IEC 27001 is a standard that specifies the requirements for establishing, implementing, maintaining and continually improving an information security management system within the context of the organization.
ISO/IEC 27002 is a standard that provides a code of practice for information security controls, but it does not provide specific guidance for cloud services. NIST SP 800-146 is a publication that provides an overview of cloud computing, its characteristics, service models, deployment models, and security considerations, but it does not provide a standard for selecting controls for cloud services. CSA CCM is a framework that provides detailed understanding of security concepts and principles that are aligned to the Cloud Security Alliance guidance in 13 domains, but it is not a standard that is based on ISO/IEC 27001. References:
* ISO/IEC 27017:2015
* [ISO/IEC 27001:2013]
* [ISO/IEC 27002:2013]
* [NIST SP 800-146]
* [CSA CCM]

According to the blog article "Continuous Auditing and Continuous Certification" by the Cloud Security Alliance, a certification target helps in the formation of a continuous certification framework by incorporating the scope description and security attributes to be tested1 A certification target is a set of security objectives that a cloud service provider (CSP) defines and commits to fulfill as part of the continuous certification process1 Each security objective is associated with a policy that specifies the assessment frequency, such as every four hours, every day, or every week1 A certification target also includes a set of tools that are capable of verifying that the security objectives are met, such as automated scripts, APIs, or third-party services1 The other options are not correct because:
* Option A is not correct because the service level objective (SLO) and service qualitative objective (SQO) are not part of the certification target, but rather part of the service level agreement (SLA) between the CSP and the cloud customer. An SLO is a measurable characteristic of the cloud service, such as availability, performance, or reliability. An SQO is a qualitative characteristic of the cloud service, such as security, privacy, or compliance2 The SLA defines the expected level of service and the consequences of not meeting it. The SLA may be used as an input for defining the certification target, but it is not equivalent or synonymous with it.
* Option C is not correct because the frequency of evaluating security attributes is not the only component of the certification target, but rather one aspect of it. The frequency of evaluating security attributes is determined by the policy that is associated with each security objective in the certification target. The policy defines how often the security objective should be verified by the tools, such as every four hours, every day, or every week1 However, the frequency alone does not define the certification target, as it also depends on the scope description and the security attributes to be tested.
* Option D is not correct because CSA STAR level 2 attestation is not a component of the certification target, but rather a prerequisite for it. CSA STAR level 2 attestation is a third-party independent assessment of the CSP's security posture based on ISO/IEC 27001 and CSA Cloud Controls Matrix (CCM)3 CSA STAR level 2 attestation provides a baseline assurance level for the CSP before they can define and implement their certification target for continuous certification. CSA STAR level 2 attestation is also required for CSA STAR level 3 certification, which is based on continuous auditing and continuous certification3 References: 1: Continuous Auditing and Continuous Certification - Cloud Security Alliance 2: Service Level Agreement | CSA 3: Open Certification Framework | CSA - Cloud Security Alliance