Software Engineer, Security

Keycard is hiring a staff-level Software Engineer, Security to secure its agent identity and access product and the company’s own systems. The role combines production software engineering with threat modeling, design and code review, adversarial testing, cloud security controls, and incident response.

Responsibilities:

• Threat modeling. Trace how an agent gets access, from token exchange through delegation to the per-tool check at our MCP gateway, then attack it: confused deputies, poisoned tool descriptions, prompt injection, issuer and audience mix-ups, token passthrough. Credentials shouldn't leak between hops, and delegated access should end when it expires or is revoked
• Assume compromise. Even a compromised agent should be stopped from escalating privileges or crossing tenants. Document what it can still do with its access
• Design review. Review designs and code across the token service, Cedar policy engine, MCP gateway, CLI, SDKs, and Console, mostly for who can do what and whether zones stay isolated
• Attack with agents. Run scoped agents against an isolated instance and chase the authorization failures they find. Confirmed failures become CI regressions for token exchange, impersonation, or per-tool policy. Example: a harness that follows a delegated credential end to end and checks it never gains scope or lifetime
• Customer reviews. Be the technical voice when customers' security teams review or pentest us; operations runs the process
• Cloud guardrails. Set the rules for our cloud accounts, pipeline, and customer-hosted cells, down to cell isolation and audited break-glass access. Platform engineering builds them
• Our own credentials. Keep them short-lived and narrow. Design service identity and PKI, sign what we ship to customers, and manage dependency risk. You also use Keycard to scope what our own agents can reach
• Incident response. Investigate vulnerabilities and security events, coordinate fixes, and improve detection. You'll also work out with engineering how on-call works for security

Requirements:

• You've shipped and maintained production code, not only security tooling, and you've found and fixed vulnerabilities in applications or identity systems
• You can read unfamiliar code, build an exploit or reproduction, and ship the fix with a regression test
• You know OAuth 2.0 and 2.1, OIDC, and token exchange (RFC 8693), and can describe failures you've seen, like refresh-token misuse
• You can spot the problem in an IAM policy, a network path, or a cloud audit log, even if you've never run cloud infrastructure
• Good judgment about risk. You can explain an attack path, size it, and agree on a fix with the team
• Agents at work. You use agents for review, triage, or testing, and know how to check their output and limit their access
• Experience in identity infrastructure, developer tools, or multi-tenant SaaS
• Experience with DPoP, Cedar, or SPIFFE/SPIRE
• Hands-on AWS security: IAM, SCPs, logging, infrastructure as code
• Securing agents or MCP servers, including tool permissions and sandboxing
• A security tool you built that engineers adopted and that ended a class of bugs
• Public security work: CVEs, bug bounties, write-ups, or OAuth and MCP standards work