MCP 2b-1: session-to-agent binding + dual-key rotation#28
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First slice of #17's [2b] items: - SessionPin { identity_id, agent_id } replaces the plain identity string in the session cache. A session ID presented by a different agent (or by a different mode: agent vs network-trust) is rejected with 403 — session IDs are not portable between agents. - Dual keys: [[mcp.agents]] accepts keys = [...] alongside key = ... (both merged at load) so two keys can be simultaneously valid for zero-downtime rotation. Config load fails loudly when an agent has no key at all. - Pin log line now includes the owning agent. Closes the '[2b] Session-to-agent binding' gate item (the session-cannot- outlive-credential half lands with the App backend slice) and the dual-key rotation open question from 2a. 45 tests (3 new: cross-agent session rejection, mode-mismatch rejection, rotation accepting both keys with identical policy).
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* 2b-1: session-to-agent binding + dual-key rotation First slice of #17's [2b] items: - SessionPin { identity_id, agent_id } replaces the plain identity string in the session cache. A session ID presented by a different agent (or by a different mode: agent vs network-trust) is rejected with 403 — session IDs are not portable between agents. - Dual keys: [[mcp.agents]] accepts keys = [...] alongside key = ... (both merged at load) so two keys can be simultaneously valid for zero-downtime rotation. Config load fails loudly when an agent has no key at all. - Pin log line now includes the owning agent. Closes the '[2b] Session-to-agent binding' gate item (the session-cannot- outlive-credential half lands with the App backend slice) and the dual-key rotation open question from 2a. 45 tests (3 new: cross-agent session rejection, mode-mismatch rejection, rotation accepting both keys with identical policy). * 2b-2: write classification + per-agent repo allowlists Second slice of #17's [2b] items (stacked on 2b-1): - src/policy.rs: rule-based tool classification — Read iff get_*/list_*/ search_*/*_read (matches the observed /readonly surface), everything else including unknown names is Write (conservative: misclassifying a read is an inconvenience, misclassifying a write would be a security bug). Repo resolution from tool arguments (owner+repo) and allowlist matching (owner/repo exact, owner/* wildcard, case-insensitive, malformed entries fail closed). - Enforcement for authenticated agents on tools/call, in order: tool allowlist -> write classification (ALL writes 403 until 2b-5's enable switch, even if allowlisted — closes the operator-typo gap) -> repo allowlist with deny-if-unresolvable. - repos = [] means unrestricted (additional constraint, keeps 2a configs working). Phase 1 no-agent mode is untouched (readonly upstream is its write barrier). - Audit lines now include the resolved repo: MCP tools/call issue_read repo=openabdev/ghpool [agent=... via ...] 59 tests (14 new: 7 policy unit, 7 integration incl. allowlisted-write blocked, wildcard match, deny-unresolvable, 2a backward compat). * Merge main (squash-merged #28) --------- Co-authored-by: chaodu-agent <chaodu-agent@users.noreply.github.com>
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Summary
First slice of #17's
[2b]gate items (per the delivery plan: 2b ships as a stacked sequence — this is the smallest, purely-local piece).Changes
SessionPin { identity_id, agent_id }. A session ID presented by a different agent — even one holding a valid key of its own — gets403 session not owned by this agent, audit-logged as a binding violation. Mode mismatches (a Phase 1 no-agent session presented in agent mode, or vice versa) are also rejected. The response does not disclose whether the session exists.[[mcp.agents]]acceptskeys = [...]alongside (or instead of)key = ...; all entries are secret-ref-resolved and simultaneously valid, enabling add-new → roll-over → remove-old rotation with zero downtime. An agent with no keys at all fails config load loudly.MCP session pinned to identity zz [agent=kiro-zz] [session=…].Why binding matters even with per-request policy checks
Tool-allowlist enforcement is per-request against the presenting agent's policy, so there was no privilege escalation — but without binding, agent B could ride agent A's session (consuming its pinned identity/budget and polluting audit attribution). Now the session owner is part of the authz decision.
Tested
45 tests (3 new): cross-agent session rejection (valid key, wrong session → 403, upstream never sees it; rightful owner unaffected), mode-mismatch rejection, dual-key rotation (both keys valid, resolving to the same policy). Clippy
-D warningsclean.Remaining 2b slices
2b-2 write classification + repo allowlists → 2b-3 GitHub App backend (incl. session-credential lifetime) → 2b-4 fail-closed audit → 2b-5 enable writes.