## 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
MCP authorization spec distinguishes insufficient_scope challenges from other auth failures; hosts must implement step-up rather than expiry UX.
## Steps
1. Capture status and WWW-Authenticate header.
2. If insufficient_scope: start authorization with requested scopes from the challenge.
3. Retry the tool call with the upgraded token.
4. Only treat 401 invalid/expired as re-login/expiry paths.
## Expected result
Client requests broader scopes and retries successfully instead of reporting false expiry.
## Misleading approaches
- Deleting tokens on every 403.
- Retrying the same token without scope change.
## Limitations
- Host-specific bug that misreports expiry must be fixed in that host version; spec-level remediation is correct classification.
- Single reviewed public artifact in problem data.
## Unknowns
- Exact Claude Code release that fixed or still exhibits misreport.
## Evidence claims
- (documented_platform_behavior) MCP authorization challenges can use error=insufficient_scope to signal needed scopes on authorization failure. — https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/main/docs/specification/2025-11-25/basic/authorization.mdx
Proposed approach
- Problem id
- problem-auth-insufficient-scope-stepup
- Proposed action
- Parse WWW-Authenticate on 403: if error=insufficient_scope, perform step-up OAuth for the challenged scope list; do not clear tokens as expired. Distinguish from 401 invalid_token/expired.
- Applicability
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); MCP HTTP OAuth clients (e.g. Claude Code-class hosts) calling tools that need additional scopes.; affected: MCP auth-using clients that mishandle 403 insufficient_scope; fix_status: PARTIAL
- Limitations
- State
- partial
- Text
- Host-specific bug that misreports expiry must be fixed in that host version; spec-level remediation is correct classification. Single reviewed public artifact in problem data.
- 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); MCP HTTP OAuth clients (e
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