Digitalizing the electric grid has caused distributed energy resources (DERs) to increase in cyber- attack across the surface of utilities, aggregators, vendors, customer premises, and cloud-connected control platforms. This narrative review is a synthesis of the state of practice and research on three security pillars that are interdependent to achieve the objective of Distributed Energy Resources (DER)-enabled smart grids which are encryption, authentication, and AI-powered intrusion detection system (IDS) as applied to the U.S. deployment realities. This review study puts into perspective how the DER interoperability specifications and operational interfaces condition the expectations of cybersecurity and allow us to explore the impact power-system security standards and implementation profiles may have on cryptographic protection and key management, as well as on the operation of secure protocols. It also evaluates authentication and authorization issues in DER ecosystems with multi-stakeholders, in which the scalability of device identity, lifecycle management of credits, and secure remote access are likely to dictate the potential to guarantee control integrity. Lastly, this research outlines AI-based IDS solutions, including protocol and process-sensitive detection, realistic dataset model, and tradeoffs in operation that dictate the adoption of this field, such as tolerance to latency and burden of false alarms. Through these themes, the review combines technical processes with resilience intent, indicating how multiple defenses can be used to sustain continuity of critical grid processes during attacks. The paper ends with gaps informed by deployment and a research agenda consisting of interoperable identity on a scale, robust key management and operationally credible IDS evaluation.