feat: support Cloudflare Global API Key authentication

[tjuranek]

Summary

• Adds support for authenticating with Cloudflare's Global API Key via X-Auth-Email + X-Auth-Key headers, alongside the existing OAuth and Bearer token methods
• Global API Key credentials flow through GlobalOutbound props — same isolation pattern as Bearer tokens (fix: move API token injection to GlobalOutbound via props #28), never entering the dynamic worker isolate
• getUserAndAccounts is generalized to accept either auth style (backward-compatible, still accepts a plain string)
• OutboundAuth discriminated union replaces the raw apiToken: string plumbing through the executor and server, so GlobalOutbound injects the correct headers (Authorization: Bearer vs X-Auth-Email/X-Auth-Key)
• README updated with Option 3 documenting the Global API Key config, with a warning that it grants full account access

Files changed

File	Change
src/auth/types.ts	Add global_api_key variant to AuthProps union
src/auth/oauth-handler.ts	Add buildCloudflareAuthHeaders, generalize getUserAndAccounts
src/auth/api-token-mode.ts	Add isGlobalApiKey detection + handleGlobalApiKeyRequest handler
src/index.ts	Update GlobalOutbound props to support both auth types, wire up Global API Key check
src/executor.ts	Replace apiToken: string with OutboundAuth union
src/server.ts	Add getOutboundAuth helper, pass OutboundAuth to executor
README.md	Add Option 3: Global API Key section

Test plan

• isGlobalApiKey correctly detects X-Auth-Email + X-Auth-Key headers (5 test cases)
• buildCloudflareAuthHeaders returns correct headers for both auth types (2 test cases)
• Existing isDirectApiToken, extractBearerToken, buildAuthProps tests still pass (unchanged)
• Executor tests updated to use OutboundAuth type instead of raw string
• Tested locally with wrangler dev — Global API Key request successfully authenticates, tools/list returns both tools, execute tool runs code against the Cloudflare API
• Bearer token and OAuth paths unaffected (no breaking changes)
• All 76 tests pass, npm run check clean (format, lint, typecheck, test)

🤖 Generated with Claude Code

[tjuranek]

Hey — I know this is an AI-assisted PR so I want to be upfront about that, but the motivation is
very real: I've been using the MCP server and kept hitting permission issues with scoped API
tokens. Getting the right combination of permissions configured for everything I want to do through
the agent is painful, and the Global API Key just works out of the box.

I realize it's a tradeoff — the Global API Key is less secure since it grants full account access —
but until there's an easier way to configure broad permissions on scoped tokens, I think it's a
useful option to have alongside the existing methods. The README warns about the risk.

Happy to make any changes needed to get this mergeable. Let me know if there's anything you'd want
done differently.

[mattzcarey]

Why cant you use user or account api tokens?