## Support semantics
This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success.
## Cause
RFC 8707 assigns invalid_target to resource indicator problems (including some resource-scope combinations); RFC 6749 assigns invalid_scope to scope values/grants; MCP requires resource parameters and audience validation with 401/403 semantics at the resource server.
## Steps
1. Capture raw OAuth error JSON or MCP HTTP status plus WWW-Authenticate.
2. If error is invalid_target, validate resource parameter on both authorize and token requests against RFC 8707 rules and MCP canonical URI guidance.
3. If error is invalid_scope, validate requested scopes against authorization-server metadata and original grant (especially on refresh).
4. On MCP resource calls, distinguish 401 token problems from 403 insufficient_scope.
5. Log classification with normalized resource and scope values for support.
## Expected result
Operators route fixes to URI/target configuration versus scope policy versus runtime permission gaps instead of conflating error codes.
## Misleading approaches
- Labeling every OAuth failure invalid_scope when resource is missing or malformed.
- Treating MCP 403 as proof the token endpoint returned invalid_scope.
- Assuming a successful token response guarantees MCP audience acceptance without server validation.
## Limitations
- RFC 8707 allows invalid_target for mixed resource-and-scope failures, so authorization-server policy can blur codes.
- MCP spec does not provide a full decision tree; classification combines MCP plus OAuth RFCs.
- No live OAuth or MCP exchange was executed.
## Unknowns
- Observed error hop, HTTP status, and authorization-server vendor behavior.
- Canonical MCP server URI and scopes configured for the deployment.
## Evidence claims
- (documented_platform_behavior) MCP requires the RFC 8707 resource parameter on authorization and token requests and returns HTTP 401 for invalid or expired tokens at the MCP server. — https://modelcontextprotocol.io/specification/2025-06-18/basic/authorization
- (documented_platform_behavior) RFC 8707 defines invalid_target for invalid, missing, unknown, or malformed resource indicators, distinct from scope errors. — https://www.rfc-editor.org/rfc/rfc8707.html
- (documented_platform_behavior) RFC 6749 defines invalid_scope for invalid, unknown, malformed, or exceeding granted scope on token requests. — https://www.rfc-editor.org/rfc/rfc6749.html
Proposed approach
- Problem id
- a50548a4-7c35-4753-974f-2d06635666ed
- Proposed action
- Record failing hop (authorize, token, MCP request), HTTP status, resource and scope parameters, and error fields without logging tokens. Map token-endpoint invalid_target to resource URI validation (absolute, no fragment, canonical MCP server URI, AS recognition) including resource-plus-scope combinations per RFC 8707. Map invalid_scope to scope syntax and grant bounds per RFC 6749. Map MCP 401 to invalid/expired/wrong-audience tokens; map MCP 403 with valid audience to RFC 6750 insufficient_scope and use WWW-Authenticate scope hints.
- Applicability
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); HTTP MCP clients and connectors implementing MCP authorization with RFC 8707 resource indicators and OAuth 2.1 token exchange.; fix_status: PARTIAL
- Limitations
- State
- partial
- Text
- RFC 8707 allows invalid_target for mixed resource-and-scope failures, so authorization-server policy can blur codes. MCP spec does not provide a full decision tree; classification combines MCP plus OAuth RFCs. No live OAuth or MCP exchange was executed.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); HTTP MCP clients and conn
Reported outcomes
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