Kubernetes Nginx Ingress多主机配置Azure OAuth2遇CORS错误求助

问题场景 #

在AKS环境中为dev.example.com和api.dev.example.com配置Nginx Ingress+Azure OAuth2认证，Azure AD应用配置完成后登录流程正常，但主应用访问https://api.dev.example.com/identity/.well-known/openid-configuration时触发CORS错误：预检请求的响应包含重定向，不符合CORS策略。

现有配置 #

应用Ingress配置 #

kind: Ingress
apiVersion: networking.k8s.io/v1
metadata:
  name: dev-ingress
  annotations:
    cert-manager.io/issuer: letsencrypt-cert
    kubernetes.io/ingress.class: nginx
    nginx.ingress.kubernetes.io/auth-signin: https://$host/oauth2/start?rd=$escaped_request_uri
    nginx.ingress.kubernetes.io/auth-url: https://$host/oauth2/auth
    nginx.ingress.kubernetes.io/ssl-redirect: 'false'
    nginx.ingress.kubernetes.io/use-regex: 'true'
spec:
  tls:
    - hosts:
        - dev.example.com
        - api.dev.example.com
      secretName: letsencrypt-cert
  rules:
    - host: dev.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: dev-service
                port:
                  number: 80
    - host: api.dev.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: api-service
                port:
                  number: 80

OAuth2 Proxy配置 #

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    k8s-app: oauth2-proxy
  name: oauth2-proxy
  namespace: dev
spec:
  replicas: 1
  selector:
    matchLabels:
      k8s-app: oauth2-proxy
  template:
    metadata:
      labels:
        k8s-app: oauth2-proxy
    spec:
      containers:
      - args:
        - --provider=oidc
        #- --provider=azure
        - --azure-tenant=xxxxxxxxxxxxxx
        - --skip-jwt-bearer-tokens=true
        - --skip-auth-preflight=true        
        - --email-domain=*
        - --http-address=0.0.0.0:4180
        - --cookie-domain=.example.com
        - --whitelist-domain=.example.com
        - --oidc-issuer-url=https://login.microsoftonline.com/xxxxxxxx/v2.0
        env:
        - name: OAUTH2_PROXY_CLIENT_ID
          valueFrom:
            secretKeyRef:
              name: client-id
              key: oauth2_proxy_client_id
        - name: OAUTH2_PROXY_CLIENT_SECRET
          valueFrom:
            secretKeyRef:
              name: client-secret
              key: oauth2_proxy_client_secret
        - name: OAUTH2_PROXY_COOKIE_SECRET
          valueFrom:
            secretKeyRef:
              name: cookie-secret
              key: oauth2_proxy_cookie_secret
        image: quay.io/oauth2-proxy/oauth2-proxy:latest
        imagePullPolicy: Always
        name: oauth2-proxy
        ports:
        - containerPort: 4180
          protocol: TCP
---
apiVersion: v1
kind: Service
metadata:
  labels:
    k8s-app: oauth2-proxy
  name: oauth2-proxy
  namespace: dev
spec:
  ports:
  - name: http
    port: 4180
    protocol: TCP
    targetPort: 4180
  selector:
    k8s-app: oauth2-proxy
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: oauth2-proxy
  namespace: dev
spec:
  ingressClassName: nginx
  rules:
  - host: dev.example.com
    http:
      paths:
      - path: /oauth2
        pathType: Prefix
        backend:
          service:
            name: oauth2-proxy
            port:
              number: 4180
  - host: api.dev.example.com
    http:
      paths:
      - path: /oauth2
        pathType: Prefix
        backend:
          service:
            name: oauth2-proxy
            port:
              number: 4180

问题原因与解决方案 #

核心原因 #

当前Ingress为整个api.dev.example.com配置了全局OAuth2认证，包括/identity/.well-known/openid-configuration端点。浏览器发送的OPTIONS预检请求被Ingress转发到OAuth2 Proxy认证，而认证流程会触发重定向，违反CORS规则（预检请求不允许重定向）。

具体修复步骤 #

1. 修改应用Ingress，豁免特定端点的认证并配置CORS
   在dev-ingress的annotations中添加认证豁免规则和CORS相关配置，更新后的metadata.annotations如下：

   metadata:
     name: dev-ingress
     annotations:
       cert-manager.io/issuer: letsencrypt-cert
       kubernetes.io/ingress.class: nginx
       nginx.ingress.kubernetes.io/auth-signin: https://$host/oauth2/start?rd=$escaped_request_uri
       nginx.ingress.kubernetes.io/auth-url: https://$host/oauth2/auth
       nginx.ingress.kubernetes.io/ssl-redirect: 'false'
       nginx.ingress.kubernetes.io/use-regex: 'true'
       # 豁免OpenID配置端点的认证
       nginx.ingress.kubernetes.io/auth-except: /identity/.well-known/openid-configuration
       # 启用CORS并允许主域跨域请求
       nginx.ingress.kubernetes.io/enable-cors: "true"
       nginx.ingress.kubernetes.io/cors-allow-origin: "https://dev.example.com"
       nginx.ingress.kubernetes.io/cors-allow-methods: "GET, OPTIONS"
       nginx.ingress.kubernetes.io/cors-allow-credentials: "true"
   

2. 确认OAuth2 Proxy的预检请求跳过配置
   现有配置中已包含--skip-auth-preflight=true参数，该参数会让OAuth2 Proxy直接放行OPTIONS预检请求，需确保此配置未被修改。

3. 重新应用Ingress配置
   执行命令更新Ingress资源：

   kubectl apply -f dev-ingress.yaml -n dev
   

额外说明 #

• 若api.dev.example.com还有其他需跨域的端点，可在auth-except中用逗号分隔添加，例如/identity/.well-known/openid-configuration,/api/public/*
• CORS规则需根据实际业务调整，比如允许的Origin、HTTP方法等
• 确保后端api-service能正确处理OPTIONS请求，返回合法的CORS响应头

内容的提问来源于stack exchange，提问作者Trav Erse