Securing AI agent identity with X.509 PKI on AWS
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This article presents a reference architecture for securing AI agent identities using X.509 Public Key Infrastructure (PKI) on AWS, addressing the lack of built-in authentication in the Model Context Protocol (MCP). The solution integrates Keyfactor EJBCA with AWS services like Amazon Bedrock and Secrets Manager to establish cryptographic trust between users, agents, and tools. It employs four key mechanisms: signed request envelopes for proof-of-possession, user-signed delegation assertions to avoid credential sharing, RFC 8693 audience-scoped tokens to limit exposure, and real-time OCSP revocation checks. The architecture implements three authentication layers that validate identity, ensure request freshness via nonces, and prevent replay attacks through strict timestamping. Private keys are generated locally and never transmitted, ensuring that agents act only with authorized, short-lived credentials. This approach provides a zero-trust framework where revoking a single user certificate immediately invalidates all downstream agent authority. The design is framework-agnostic and can be adapted for various multi-agent systems requiring robust security.
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