Some MCP OAuth providers (notably Supabase) return a client_secret from
dynamic client registration but omit token_endpoint_auth_method. The MCP
SDK defaults the missing method to "none", so the token exchange omits
client_secret and the server rejects it (HTTP 422 "Required parameter:
client_secret"), looping the browser consent page.
This resolves the whole class, not just one provider:
- Storage layer (HermesTokenStorage): coerce secret-bearing client info
with missing/none auth method to client_secret_post on both read and
write, persisting the corrected shape.
- Both live provider paths (tools/mcp_oauth.py HermesOAuthClientProvider
and tools/mcp_oauth_manager.py HermesMCPOAuthProvider): coerce
in-memory client info immediately before token exchange and refresh.
- Accept the full 2xx range on token and refresh responses (Supabase
returns 201 Created), instead of the SDK's exact-200 check.
- Redact token response bodies from error messages and logs on
malformed responses.
The Figma-specific request-time default (apply_oauth_provider_defaults)
remains; this generalizes the same bug class for every DCR provider.
Fixes#29680. Supersedes #34274 and #35700 (201-only variants).
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