Security is not a feature is a concern, which is co-related with the quality of your solution, what's the best way to know the quality? Measure it.

Start with the four key metrics (from DevOps Research and Assessment (DORA) )

• Deployment frequency:
• Lead time for changes
• Change failure rate
• Time to restore service

Locate your instrumentation points

• Commit timestamp
• Deployment timestamp
• Monitor service failures

Quality attributes

• Functional suitability
• Performance efficiency
  • Time behavior (Response time)
  • Resource utilization
  • Capacity (TPS - Throughput)
• Compatibility
• Usability

Testing Pyramid

• Base layer, made of the easiest tests, unit tests
• Middle layer, integration tests
• Top layer, security, performance E2E tests.

Measure code-related metrics

• Technical debt, including cohesion, modularity

To define security, it has become common to use Confidentiality, Integrity and Availability, also known as the CIA triad.

Authentication usually performed with something that you know, you have and you are (like biometrics/fingerprints)

Identify

• Risks
• Vulnerabilities
• Likelihood
• Threats

Service-Level Agreement (SLA)

The cloud computing service-level agreement (cloud SLA) is an agreement between a cloud service provider and a cloud service customer based on a taxonomy of cloud computing– specific terms to set the quality of the cloud services delivered. It characterizes quality of the cloud services delivered in terms of a set of measurable properties specific to cloud computing (business and technical) and a given set of cloud computing roles (cloud service customer, cloud service provider, and related sub-roles).

Think of a rule book and legal contract—that combination is what you have in a service-level agreement (SLA). Let us not underestimate or downplay the importance of this document/ agreement. In it, the minimum level of service, availability, security, controls, processes, communications, support and many other crucial business elements are stated and agreed to by both parties.

The purpose of an SLA is to document specific parameters, minimum service levels and remedies for any failure to meet the specified requirements. It should also affirm data ownership and specify data return and destruction details. Other important SLA points to consider include the following:

Cloud system infrastructure details and security standards
Customer right to audit legal and regulatory compliance by the CSP         
Rights and costs associated with continuing and discontinuing service use
Service availability
Service performance
Data security and privacy
Disaster recovery processes
Data location
Data access
Data portability
Problem identification and resolution expectations
Change management processes
Dispute mediation processes
Exit strategy 

Defense in Depth

Defense in depth uses a layered approach when designing the security posture of an organization. Think about a castle that holds the crown jewels. The jewels will be placed in a vaulted chamber in a central location guarded by security guards. The castle is built around the vault with additional layers of security—soldiers, walls, a moat. The same approach is true when designing the logical security of a facility or system. Using layers of security will deter many attackers and encourage them to focus on other, easier targets.

Defense in depth provides more of a starting point for considering all types of controls—administrative, technological, and physical—that empower insiders and operators to work together to protect their organization and its systems.

Here are some examples that further explain the concept of defense in depth:

Data: Controls that protect the actual data with technologies such as encryption, data leak prevention, identity and access management and data controls.
Application: Controls that protect the application itself with technologies such as data leak prevention, application firewalls and database monitors.
Host: Every control that is placed at the endpoint level, such as antivirus, endpoint firewall, configuration and patch management.
Internal network: Controls that are in place to protect uncontrolled data flow and user access across the organizational network. Relevant technologies include intrusion detection systems, intrusion prevention systems, internal firewalls and network access controls.
Perimeter: Controls that protect against unauthorized access to the network. This level includes the use of technologies such as gateway firewalls, honeypots, malware analysis and secure demilitarized zones (DMZs).
Physical: Controls that provide a physical barrier, such as locks, walls or access control.
Policies, procedures and awareness: Administrative controls that reduce insider threats (intentional and unintentional) and identify risks as soon as they appear. 

Top 10 tips for a secure SDLC (shift-left):

• Measure time spent for issues remediation
• Identify performance bottlenecks, pain points between processes, people and tools.
• Make small incremental changes
• Automate scans and the most useful/common processes.
• Update and improve workflows
• Demonstrate compliance, make sure there's consistency across temas and environments.
• Generate security reports, leverage tools like SAST and DAST.
• Empower the teams with security dashboards, and AI or assisted tools to work smarter towards security.
• Streamline the toolchain, reduce/ditch the toolchain.

• https://www.cisa.gov/free-cybersecurity-services-and-tools