A2A, or agent-to-agent communication, describes interactions where one AI agent delegates work to another agent. These flows can be stateful, multi-step, and policy sensitive, so organisations need authentication, tracing, and guardrails to prevent uncontrolled delegation, unsafe data sharing, and opaque decision chains.
Expanded Definition
A2A, or agent-to-agent communication, is the controlled exchange of tasks, context, and results between autonomous software entities that each have execution authority and tool access. In NHI governance, the term matters because an agent does not merely send a message, it may delegate work, transfer context, and trigger downstream actions that alter data, workflows, or access decisions.
Definitions vary across vendors and emerging standards: some implementations treat A2A as a simple message bus pattern, while others treat it as a policy-governed delegation model with identity, authorization, and traceability requirements. For that reason, practitioners should align A2A with the security expectations described in the NIST Cybersecurity Framework 2.0 and with the broader NHI lifecycle guidance in Ultimate Guide to NHIs. The practical difference from ordinary service-to-service traffic is that A2A often involves dynamic delegation chains, variable tool use, and decisions that are not fully predetermined at design time.
The most common misapplication is treating agent handoffs as ordinary API calls, which occurs when organisations skip per-hop authentication, scope checks, and trace logging for delegated actions.
Examples and Use Cases
Implementing A2A rigorously often introduces more policy checks and observability overhead, requiring organisations to weigh autonomous coordination against tighter control of delegation and data flow.
- An orchestration agent assigns a remediation task to a specialist agent that can only inspect approved ticket data before proposing a fix.
- A research agent forwards a summarisation task to another agent, but the receiving agent is restricted from seeing raw customer secrets or internal prompts.
- A finance workflow uses one agent to gather evidence and another to validate controls, with each hop logged for audit and rollback.
- A support triage agent delegates to a retrieval agent that queries a knowledge base, but the result must pass policy validation before being returned to the user.
- An enterprise platform applies A2A only within a trusted boundary, using the governance model described in the Ultimate Guide to NHIs so each agent identity remains attributable across the chain.
These patterns are still evolving, so organisations should document where the handoff boundary sits, what context may be shared, and which agent is accountable for the downstream result. That mapping should be paired with the identity and access assumptions in NIST Cybersecurity Framework 2.0 rather than left to implementation convenience.
Why It Matters in NHI Security
A2A changes the risk profile of agentic systems because compromise at one agent can cascade into unauthorized delegation, broader secret exposure, and opaque decision chains. When agent identities are not governed as NHIs, teams lose visibility into which agent requested what, which credentials were used, and whether a downstream action was legitimate. That is especially dangerous in environments where NHIs already outnumber human identities by 25x to 50x, and only 5.7% of organisations have full visibility into their service accounts, as reported in the Ultimate Guide to NHIs.
Security programs should therefore treat A2A as a governance problem, not just an integration pattern. Controls need to cover agent authentication, least privilege, step-up approval for sensitive delegation, and immutable traces that show how an action moved across agents. The same principles reflected in NIST Cybersecurity Framework 2.0 apply here, but they must be translated into agent-level identity and policy enforcement.
Organisations typically encounter the cost of weak A2A controls only after an agent chain leaks data, performs an unintended action, or becomes impossible to audit, at which point the term becomes operationally unavoidable to address.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Agentic AI Top 10, OWASP Non-Human Identity Top 10 and CSA MAESTRO address the attack and risk surface, while NIST CSF 2.0 and NIST Zero Trust (SP 800-207) set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Agentic AI Top 10 | AGENT-01 | A2A is central to agent delegation, tool use, and chained actions in agentic systems. |
| OWASP Non-Human Identity Top 10 | NHI-01 | A2A depends on governing agent identities as non-human identities with traceable authority. |
| NIST CSF 2.0 | PR.AC | Agent-to-agent exchanges require access control and identity verification across trust boundaries. |
| NIST Zero Trust (SP 800-207) | SA-8 | Zero Trust calls for continuous verification of every requesting entity, including agents. |
| CSA MAESTRO | MAESTRO addresses agentic orchestration and control-plane governance for autonomous systems. |
Require authenticated, policy-checked agent handoffs before any delegated task or tool invocation.
