Allow MCPRemoteProxy to work without upstream or client auth

[aron-muon]

Summary

MCPRemoteProxy required OIDC authentication and always injected upstream tokens when the
embedded auth server was configured. This made two common deployment patterns impossible
and the transparent proxy could not reach upstream servers behind HTTP redirects.

Why: Operators sometimes need to proxy third-party public MCP servers (e.g., documentation APIs)
with client authentication (Okta, GitHub) but without injecting tokens upstream — the upstream
is public and doesn't expect auth headers. Additionally, third-party servers may use HTTP
redirects (API gateways, scheme changes, path canonicalization) that the proxy must follow
transparently.

What changed (3 commits):

1. Add disableUpstreamTokenInjection — when true, the embedded auth server still
   handles OAuth flows for clients but does not inject upstream IdP tokens into outgoing
   requests. A strip-auth middleware removes the client's ToolHive JWT from the
   Authorization header to prevent it leaking to the upstream.

2. Make oidcConfig optional — when omitted, the proxy allows anonymous access with no
   authentication on either side.

3. Fix transparent proxy for remote servers behind redirects — three issues prevented
   MCPRemoteProxy from connecting to third-party upstreams that use redirects:

   • X-Forwarded-Host leaked the proxy's hostname; the upstream used it to build 307
     redirect URLs pointing back to the proxy (redirect loop). Fix: skip SetXForwarded()
     for remote upstreams.
   • Go's http.Transport.RoundTrip does not follow redirects, but httputil.ReverseProxy
     uses Transport directly. Fix: add forwardFollowingRedirects that follows up to 10
     redirects, preserving method/body for 307/308 (RFC 7538).
   • Adds debug logging for outbound request headers and upstream response status codes.

Type of change

• New feature
• Bug fix

Test plan

• Unit tests (task test)
• Linting (task lint-fix)
• Manual testing (describe below)

Deployed MCPRemoteProxy with embedded auth server + disableUpstreamTokenInjection: true
proxying a public third-party MCP server behind an API gateway that 307-redirects
(HTTPS→HTTP scheme change). Verified:

• Client OAuth flow via Okta completes successfully
• Proxy follows upstream 307 redirects transparently (logged at WARN)
• MCP initialize returns 200 from the final upstream destination
• tools/list, prompts/list, resources/list all return 200
• Cedar authorization evaluates correctly against ToolHive JWTs
• Authorization header is stripped before forwarding to the public upstream

Changes

File	Change
api/v1alpha1/mcpexternalauthconfig_types.go	Add DisableUpstreamTokenInjection to EmbeddedAuthServerConfig CRD
pkg/authserver/config.go	Add DisableUpstreamTokenInjection to runtime RunConfig
pkg/runner/middleware.go	Add strip-auth middleware; skip upstream swap when injection disabled
pkg/runner/middleware_test.go	Tests for strip-auth and upstream swap middleware selection
controllerutil/authserver.go	Wire CRD field through to RunConfig
api/v1alpha1/mcpremoteproxy_types.go	Make OIDCConfig optional (value to pointer)
controllers/mcpremoteproxy_controller.go	Add nil guard for OIDC validation
controllers/mcpremoteproxy_deployment.go	Add nil guard for OIDC env vars
controllers/mcpremoteproxy_runconfig.go	Extract auth config helper, skip OIDC when nil
proxy/transparent/transparent_proxy.go	Skip SetXForwarded() for remote upstreams; add forwardFollowingRedirects; add outbound/response debug logging

Does this introduce a user-facing change?

Yes. Three new capabilities for MCPRemoteProxy:

1. Anonymous proxy: Omit oidcConfig to allow unauthenticated access to a proxied MCP server.
2. Embedded auth without upstream injection: Set disableUpstreamTokenInjection: true on an embeddedAuthServer MCPExternalAuthConfig to authenticate clients without injecting tokens upstream.
3. Transparent redirect following: The proxy now follows HTTP 3xx redirects from upstream servers automatically, enabling proxying of MCP servers behind API gateways or CDNs that redirect.

Large PR Justification

• ~700 of the changed lines are generated code (CRD manifests, deepcopy, swagger docs) that cannot be split from the source changes
• The remaining hand-written code includes the three tightly coupled features (all address the same gap: MCPRemoteProxy for third-party public MCP servers) plus required test updates for the value-to-pointer type change

Generated with Claude Code

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## Large PR Justification

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[codecov]

Codecov Report

❌ Patch coverage is 42.74809% with 75 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.40%. Comparing base (6bb814d) to head (49e9690).

Files with missing lines	Patch %	Lines
...g/transport/proxy/transparent/transparent_proxy.go	31.14%	36 Missing and 6 partials ⚠️
pkg/runner/middleware.go	22.72%	15 Missing and 2 partials ⚠️
...-operator/controllers/mcpremoteproxy_deployment.go	59.09%	2 Missing and 7 partials ⚠️
...v-operator/controllers/mcpremoteproxy_runconfig.go	65.00%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4168      +/-   ##
==========================================
- Coverage   68.95%   68.40%   -0.55%     
==========================================
  Files         467      467              
  Lines       46981    47130     +149     
==========================================
- Hits        32395    32239     -156     
- Misses      11965    12072     +107     
- Partials     2621     2819     +198     

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[github-actions]

✅ Large PR justification has been provided. The size review has been dismissed and this PR can now proceed with normal review.