P1-3: JWT auth + OIDC (Entra ID / Google Workspace / Okta) for proxy clients

Problem

Today proxy auth is `Authorization: Bearer <static_api_key>` only (`crates/aisix-proxy/src/auth.rs:1-139`). Enterprise customers using SSO need JWT verification — the bearer becomes an OIDC ID token signed by their IdP (Entra ID / Google Workspace / Okta / Auth0 / Keycloak / generic OIDC).

LiteLLM has full OIDC introspection; we have nothing.

Scope

DP (moonming/ai-gateway)

• Detect JWT format in the bearer (3-segment base64). If JWT shape, switch to JWT path; otherwise keep static-key path.
• Verify signature against JWKS (cached, refresh every `jwks_refresh_interval`).
• Validate `iss`, `aud`, `exp`, `nbf`. Optional: per-claim allowlist (e.g., `groups` claim must contain "ai-users").
• Map verified JWT to a virtual ApiKey-equivalent identity carrying the JWT's `sub` as the rate-limit/budget key. Optional: pre-provision `Identity` records keyed by sub for per-user budgets/limits.
• Config (etcd-loaded): `auth.jwt: { providers: [{name, jwks_url, issuer, audience, claim_mappings}] }`.

CP (api7/api7ee-3-control-plane)

• New resource `auth_provider` (env-scoped) with kind=`jwt` config.
• CRUD endpoints + push to etcd.

Dashboard UI (api7/AISIX-Cloud)

• New page "Auth providers" under Environment scope.
• Form: provider type (Entra/Google/Okta/Auth0/generic), wizard prefilling JWKS URLs from well-known IdP discovery docs.

e2e

• Mock JWKS endpoint, sign a JWT, send to DP, assert auth succeeds.
• Negative test: tampered JWT signature → 401.

Estimate

DP 4d, CP 1.5d, UI 2d, e2e 1d

Start by reading crates/aisix-proxy/src/auth.rs:1-139 and the existing etcd-loaded authentication configuration. Then trace the control-plane and dashboard authentication-provider entry points, and review the e2e setup for mock services. Done means static bearer keys still work, configured OIDC tokens are verified and mapped correctly, CRUD/configuration flows work, and both positive and tampered-signature tests pass.