Claude Code / AI Coding Tools

MCP auth validation fails: google tokeninfo returns exp as JSON string, not int64

Fix Claude Code / claude.ai OAuth authentication failure when using Google as IdP via MCP Toolbox Includes evidence for Claude Code troubleshooting demand.

Source-backed Last updated May 17, 2026 1 source Needs local verification

Category: AI Coding Tools
Error signature: failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64
Quick fix: Verify the account session, API key, provider settings, and environment where the failing tool is running.
Updated: May 17, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Claude Code, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

What this error means

failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64 is a Claude Code failure pattern reported for developers trying to fix claude code / claude.ai oauth authentication failure when using google as idp via mcp toolbox. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Issue #3240 in googleapis/mcp-toolbox (opened 2026-05-15): MCP auth with Google OIDC provider blocks all requests. Google oauth2/v3/tokeninfo returns numeric fields as quoted strings (exp, expires_in) but the Go struct declares Exp as int64 causing unmarshal panic → HTTP 500. Blocks end-to-end MCP OAuth flow documented in official docs. Category: AI Coding Tools because this directly affects Claude Code MCP connectivity — the primary user-facing symptom is Claude Code failing to authenticate.

Common causes

Issue #3240 in googleapis/mcp-toolbox (opened 2026-05-15): MCP auth with Google OIDC provider blocks all requests. Google oauth2/v3/tokeninfo returns numeric fields as quoted strings (exp, expires_in) but the Go struct declares Exp as int64 causing unmarshal panic → HTTP 500. Blocks end-to-end MCP OAuth flow documented in official docs. Category: AI Coding Tools because this directly affects Claude Code MCP connectivity — the primary user-facing symptom is Claude Code failing to authenticate.

Quick fixes

Confirm the exact error signature matches failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64.
Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
Verify the account session, API key, provider settings, and environment where the failing tool is running.

Platform/tool-specific checks

Verify the command, editor, extension, or API client that produced the error.
Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

Capture the exact error message and the command, editor action, or request that triggered it.
Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
Review the source evidence below and compare it with your environment.
Apply one change at a time and rerun the smallest failing action.
Keep the working fix documented for the team or deployment environment.

How to prevent it

Keep provider/tool configuration documented.
Record non-secret diagnostics such as tool version, provider name, model name, and command path.
Add a lightweight check before CI or production workflows depend on the tool.

Diagnostic flow for this page

Match failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64 exactly before applying the quick fix.
Compare the failing environment with Claude Code versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64 mean in Claude Code?

failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64 indicates the workflow described by "MCP auth validation fails: google tokeninfo returns exp as JSON string, not int64" failed in a AI Coding Tools context. Start by confirming the exact signature and the component that emitted it.

What should I check first for failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64?

Check whether this cause matches your environment: Issue #3240 in googleapis/mcp-toolbox (opened 2026-05-15): MCP auth with Google OIDC provider blocks all requests. Google oauth2/v3/tokeninfo returns numeric fields as quoted strings (exp, expires_in) but the Go struct declares Exp as int64 causing unmarshal panic → HTTP 500. Blocks end-to-end MCP OAuth flow documented in official docs. Category: AI Coding Tools because this directly affects Claude Code MCP connectivity — the primary user-facing symptom is Claude Code failing to authenticate.

Is the failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64 guidance source-backed?

The "MCP auth validation fails: google tokeninfo returns exp as JSON string, not int64" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64?

For "MCP auth validation fails: google tokeninfo returns exp as JSON string, not int64", avoid applying "Verify the account session, API key, provider settings, and environment where the failing tool is running." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging failed to parse introspection response: json: cannot unmarshal string into Go struct field .exp of type int64?

For "MCP auth validation fails: google tokeninfo returns exp as JSON string, not int64", collect the failing Claude Code command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.