PR #11383's consolidation fixed external-refresh reloading and 401 dedup
but left two latent bugs that surfaced on BetterStack and any other OAuth
MCP with a split-origin authorization server:
1. HermesTokenStorage persisted only a relative 'expires_in', which is
meaningless after a process restart. The MCP SDK's OAuthContext
does NOT seed token_expiry_time in _initialize, so is_token_valid()
returned True for any reloaded token regardless of age. Expired
tokens shipped to servers, and app-level auth failures (e.g.
BetterStack's 'No teams found. Please check your authentication.')
were invisible to the transport-layer 401 handler.
2. Even once preemptive refresh did fire, the SDK's _refresh_token
falls back to {server_url}/token when oauth_metadata isn't cached.
For providers whose AS is at a different origin (BetterStack:
mcp.betterstack.com for MCP, betterstack.com/oauth/token for the
token endpoint), that fallback 404s and drops into full browser
re-auth on every process restart.
Fix set:
- HermesTokenStorage.set_tokens persists an absolute wall-clock
expires_at alongside the SDK's OAuthToken JSON (time.time() + TTL
at write time).
- HermesTokenStorage.get_tokens reconstructs expires_in from
max(expires_at - now, 0), clamping expired tokens to zero TTL.
Legacy files without expires_at fall back to file-mtime as a
best-effort wall-clock proxy, self-healing on the next set_tokens.
- HermesMCPOAuthProvider._initialize calls super(), then
update_token_expiry on the reloaded tokens so token_expiry_time
reflects actual remaining TTL. If tokens are loaded but
oauth_metadata is missing, pre-flight PRM + ASM discovery runs
via httpx.AsyncClient using the MCP SDK's own URL builders and
response handlers (build_protected_resource_metadata_discovery_urls,
handle_auth_metadata_response, etc.) so the SDK sees the correct
token_endpoint before the first refresh attempt. Pre-flight is
skipped when there are no stored tokens to keep fresh-install
paths zero-cost.
Test coverage (tests/tools/test_mcp_oauth_cold_load_expiry.py):
- set_tokens persists absolute expires_at
- set_tokens skips expires_at when token has no expires_in
- get_tokens round-trips expires_at -> remaining expires_in
- expired tokens reload with expires_in=0
- legacy files without expires_at fall back to mtime proxy
- _initialize seeds token_expiry_time from stored tokens
- _initialize flags expired-on-disk tokens as is_token_valid=False
- _initialize pre-flights PRM + ASM discovery with mock transport
- _initialize skips pre-flight when no tokens are stored
Verified against BetterStack MCP:
hermes mcp test betterstack -> Connected (2508ms), 83 tools
mcp_betterstack_telemetry_list_teams_tool -> real team data, not
'No teams found. Please check your authentication.'
Reference: mcp-oauth-token-diagnosis skill, Fix A.
Hermes Agent
cc06beaf13